blob: 061673150f5d876935fc7e1db5973f18c2e66e5a [file] [log] [blame]
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import (
"internal/abi"
"internal/cpu"
"internal/goarch"
"internal/goexperiment"
"internal/goos"
"runtime/internal/atomic"
"runtime/internal/sys"
"unsafe"
)
// set using cmd/go/internal/modload.ModInfoProg
var modinfo string
// Goroutine scheduler
// The scheduler's job is to distribute ready-to-run goroutines over worker threads.
//
// The main concepts are:
// G - goroutine.
// M - worker thread, or machine.
// P - processor, a resource that is required to execute Go code.
// M must have an associated P to execute Go code, however it can be
// blocked or in a syscall w/o an associated P.
//
// Design doc at https://golang.org/s/go11sched.
// Worker thread parking/unparking.
// We need to balance between keeping enough running worker threads to utilize
// available hardware parallelism and parking excessive running worker threads
// to conserve CPU resources and power. This is not simple for two reasons:
// (1) scheduler state is intentionally distributed (in particular, per-P work
// queues), so it is not possible to compute global predicates on fast paths;
// (2) for optimal thread management we would need to know the future (don't park
// a worker thread when a new goroutine will be readied in near future).
//
// Three rejected approaches that would work badly:
// 1. Centralize all scheduler state (would inhibit scalability).
// 2. Direct goroutine handoff. That is, when we ready a new goroutine and there
// is a spare P, unpark a thread and handoff it the thread and the goroutine.
// This would lead to thread state thrashing, as the thread that readied the
// goroutine can be out of work the very next moment, we will need to park it.
// Also, it would destroy locality of computation as we want to preserve
// dependent goroutines on the same thread; and introduce additional latency.
// 3. Unpark an additional thread whenever we ready a goroutine and there is an
// idle P, but don't do handoff. This would lead to excessive thread parking/
// unparking as the additional threads will instantly park without discovering
// any work to do.
//
// The current approach:
//
// This approach applies to three primary sources of potential work: readying a
// goroutine, new/modified-earlier timers, and idle-priority GC. See below for
// additional details.
//
// We unpark an additional thread when we submit work if (this is wakep()):
// 1. There is an idle P, and
// 2. There are no "spinning" worker threads.
//
// A worker thread is considered spinning if it is out of local work and did
// not find work in the global run queue or netpoller; the spinning state is
// denoted in m.spinning and in sched.nmspinning. Threads unparked this way are
// also considered spinning; we don't do goroutine handoff so such threads are
// out of work initially. Spinning threads spin on looking for work in per-P
// run queues and timer heaps or from the GC before parking. If a spinning
// thread finds work it takes itself out of the spinning state and proceeds to
// execution. If it does not find work it takes itself out of the spinning
// state and then parks.
//
// If there is at least one spinning thread (sched.nmspinning>1), we don't
// unpark new threads when submitting work. To compensate for that, if the last
// spinning thread finds work and stops spinning, it must unpark a new spinning
// thread. This approach smooths out unjustified spikes of thread unparking,
// but at the same time guarantees eventual maximal CPU parallelism
// utilization.
//
// The main implementation complication is that we need to be very careful
// during spinning->non-spinning thread transition. This transition can race
// with submission of new work, and either one part or another needs to unpark
// another worker thread. If they both fail to do that, we can end up with
// semi-persistent CPU underutilization.
//
// The general pattern for submission is:
// 1. Submit work to the local or global run queue, timer heap, or GC state.
// 2. #StoreLoad-style memory barrier.
// 3. Check sched.nmspinning.
//
// The general pattern for spinning->non-spinning transition is:
// 1. Decrement nmspinning.
// 2. #StoreLoad-style memory barrier.
// 3. Check all per-P work queues and GC for new work.
//
// Note that all this complexity does not apply to global run queue as we are
// not sloppy about thread unparking when submitting to global queue. Also see
// comments for nmspinning manipulation.
//
// How these different sources of work behave varies, though it doesn't affect
// the synchronization approach:
// * Ready goroutine: this is an obvious source of work; the goroutine is
// immediately ready and must run on some thread eventually.
// * New/modified-earlier timer: The current timer implementation (see time.go)
// uses netpoll in a thread with no work available to wait for the soonest
// timer. If there is no thread waiting, we want a new spinning thread to go
// wait.
// * Idle-priority GC: The GC wakes a stopped idle thread to contribute to
// background GC work (note: currently disabled per golang.org/issue/19112).
// Also see golang.org/issue/44313, as this should be extended to all GC
// workers.
var (
m0 m
g0 g
mcache0 *mcache
raceprocctx0 uintptr
raceFiniLock mutex
)
// This slice records the initializing tasks that need to be
// done to start up the runtime. It is built by the linker.
var runtime_inittasks []*initTask
// main_init_done is a signal used by cgocallbackg that initialization
// has been completed. It is made before _cgo_notify_runtime_init_done,
// so all cgo calls can rely on it existing. When main_init is complete,
// it is closed, meaning cgocallbackg can reliably receive from it.
var main_init_done chan bool
//go:linkname main_main main.main
func main_main()
// mainStarted indicates that the main M has started.
var mainStarted bool
// runtimeInitTime is the nanotime() at which the runtime started.
var runtimeInitTime int64
// Value to use for signal mask for newly created M's.
var initSigmask sigset
// The main goroutine.
func main() {
mp := getg().m
// Racectx of m0->g0 is used only as the parent of the main goroutine.
// It must not be used for anything else.
mp.g0.racectx = 0
// Max stack size is 1 GB on 64-bit, 250 MB on 32-bit.
// Using decimal instead of binary GB and MB because
// they look nicer in the stack overflow failure message.
if goarch.PtrSize == 8 {
maxstacksize = 1000000000
} else {
maxstacksize = 250000000
}
// An upper limit for max stack size. Used to avoid random crashes
// after calling SetMaxStack and trying to allocate a stack that is too big,
// since stackalloc works with 32-bit sizes.
maxstackceiling = 2 * maxstacksize
// Allow newproc to start new Ms.
mainStarted = true
if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon
systemstack(func() {
newm(sysmon, nil, -1)
})
}
// Lock the main goroutine onto this, the main OS thread,
// during initialization. Most programs won't care, but a few
// do require certain calls to be made by the main thread.
// Those can arrange for main.main to run in the main thread
// by calling runtime.LockOSThread during initialization
// to preserve the lock.
lockOSThread()
if mp != &m0 {
throw("runtime.main not on m0")
}
// Record when the world started.
// Must be before doInit for tracing init.
runtimeInitTime = nanotime()
if runtimeInitTime == 0 {
throw("nanotime returning zero")
}
if debug.inittrace != 0 {
inittrace.id = getg().goid
inittrace.active = true
}
doInit(runtime_inittasks) // Must be before defer.
// Defer unlock so that runtime.Goexit during init does the unlock too.
needUnlock := true
defer func() {
if needUnlock {
unlockOSThread()
}
}()
gcenable()
main_init_done = make(chan bool)
if iscgo {
if _cgo_pthread_key_created == nil {
throw("_cgo_pthread_key_created missing")
}
if _cgo_thread_start == nil {
throw("_cgo_thread_start missing")
}
if GOOS != "windows" {
if _cgo_setenv == nil {
throw("_cgo_setenv missing")
}
if _cgo_unsetenv == nil {
throw("_cgo_unsetenv missing")
}
}
if _cgo_notify_runtime_init_done == nil {
throw("_cgo_notify_runtime_init_done missing")
}
// Set the x_crosscall2_ptr C function pointer variable point to crosscall2.
if set_crosscall2 == nil {
throw("set_crosscall2 missing")
}
set_crosscall2()
// Start the template thread in case we enter Go from
// a C-created thread and need to create a new thread.
startTemplateThread()
cgocall(_cgo_notify_runtime_init_done, nil)
}
// Run the initializing tasks. Depending on build mode this
// list can arrive a few different ways, but it will always
// contain the init tasks computed by the linker for all the
// packages in the program (excluding those added at runtime
// by package plugin). Run through the modules in dependency
// order (the order they are initialized by the dynamic
// loader, i.e. they are added to the moduledata linked list).
for m := &firstmoduledata; m != nil; m = m.next {
doInit(m.inittasks)
}
// Disable init tracing after main init done to avoid overhead
// of collecting statistics in malloc and newproc
inittrace.active = false
close(main_init_done)
needUnlock = false
unlockOSThread()
if isarchive || islibrary {
// A program compiled with -buildmode=c-archive or c-shared
// has a main, but it is not executed.
return
}
fn := main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
fn()
if raceenabled {
runExitHooks(0) // run hooks now, since racefini does not return
racefini()
}
// Make racy client program work: if panicking on
// another goroutine at the same time as main returns,
// let the other goroutine finish printing the panic trace.
// Once it does, it will exit. See issues 3934 and 20018.
if runningPanicDefers.Load() != 0 {
// Running deferred functions should not take long.
for c := 0; c < 1000; c++ {
if runningPanicDefers.Load() == 0 {
break
}
Gosched()
}
}
if panicking.Load() != 0 {
gopark(nil, nil, waitReasonPanicWait, traceBlockForever, 1)
}
runExitHooks(0)
exit(0)
for {
var x *int32
*x = 0
}
}
// os_beforeExit is called from os.Exit(0).
//
//go:linkname os_beforeExit os.runtime_beforeExit
func os_beforeExit(exitCode int) {
runExitHooks(exitCode)
if exitCode == 0 && raceenabled {
racefini()
}
}
// start forcegc helper goroutine
func init() {
go forcegchelper()
}
func forcegchelper() {
forcegc.g = getg()
lockInit(&forcegc.lock, lockRankForcegc)
for {
lock(&forcegc.lock)
if forcegc.idle.Load() {
throw("forcegc: phase error")
}
forcegc.idle.Store(true)
goparkunlock(&forcegc.lock, waitReasonForceGCIdle, traceBlockSystemGoroutine, 1)
// this goroutine is explicitly resumed by sysmon
if debug.gctrace > 0 {
println("GC forced")
}
// Time-triggered, fully concurrent.
gcStart(gcTrigger{kind: gcTriggerTime, now: nanotime()})
}
}
// Gosched yields the processor, allowing other goroutines to run. It does not
// suspend the current goroutine, so execution resumes automatically.
//
//go:nosplit
func Gosched() {
checkTimeouts()
mcall(gosched_m)
}
// goschedguarded yields the processor like gosched, but also checks
// for forbidden states and opts out of the yield in those cases.
//
//go:nosplit
func goschedguarded() {
mcall(goschedguarded_m)
}
// goschedIfBusy yields the processor like gosched, but only does so if
// there are no idle Ps or if we're on the only P and there's nothing in
// the run queue. In both cases, there is freely available idle time.
//
//go:nosplit
func goschedIfBusy() {
gp := getg()
// Call gosched if gp.preempt is set; we may be in a tight loop that
// doesn't otherwise yield.
if !gp.preempt && sched.npidle.Load() > 0 {
return
}
mcall(gosched_m)
}
// Puts the current goroutine into a waiting state and calls unlockf on the
// system stack.
//
// If unlockf returns false, the goroutine is resumed.
//
// unlockf must not access this G's stack, as it may be moved between
// the call to gopark and the call to unlockf.
//
// Note that because unlockf is called after putting the G into a waiting
// state, the G may have already been readied by the time unlockf is called
// unless there is external synchronization preventing the G from being
// readied. If unlockf returns false, it must guarantee that the G cannot be
// externally readied.
//
// Reason explains why the goroutine has been parked. It is displayed in stack
// traces and heap dumps. Reasons should be unique and descriptive. Do not
// re-use reasons, add new ones.
func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason waitReason, traceReason traceBlockReason, traceskip int) {
if reason != waitReasonSleep {
checkTimeouts() // timeouts may expire while two goroutines keep the scheduler busy
}
mp := acquirem()
gp := mp.curg
status := readgstatus(gp)
if status != _Grunning && status != _Gscanrunning {
throw("gopark: bad g status")
}
mp.waitlock = lock
mp.waitunlockf = unlockf
gp.waitreason = reason
mp.waitTraceBlockReason = traceReason
mp.waitTraceSkip = traceskip
releasem(mp)
// can't do anything that might move the G between Ms here.
mcall(park_m)
}
// Puts the current goroutine into a waiting state and unlocks the lock.
// The goroutine can be made runnable again by calling goready(gp).
func goparkunlock(lock *mutex, reason waitReason, traceReason traceBlockReason, traceskip int) {
gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceReason, traceskip)
}
func goready(gp *g, traceskip int) {
systemstack(func() {
ready(gp, traceskip, true)
})
}
//go:nosplit
func acquireSudog() *sudog {
// Delicate dance: the semaphore implementation calls
// acquireSudog, acquireSudog calls new(sudog),
// new calls malloc, malloc can call the garbage collector,
// and the garbage collector calls the semaphore implementation
// in stopTheWorld.
// Break the cycle by doing acquirem/releasem around new(sudog).
// The acquirem/releasem increments m.locks during new(sudog),
// which keeps the garbage collector from being invoked.
mp := acquirem()
pp := mp.p.ptr()
if len(pp.sudogcache) == 0 {
lock(&sched.sudoglock)
// First, try to grab a batch from central cache.
for len(pp.sudogcache) < cap(pp.sudogcache)/2 && sched.sudogcache != nil {
s := sched.sudogcache
sched.sudogcache = s.next
s.next = nil
pp.sudogcache = append(pp.sudogcache, s)
}
unlock(&sched.sudoglock)
// If the central cache is empty, allocate a new one.
if len(pp.sudogcache) == 0 {
pp.sudogcache = append(pp.sudogcache, new(sudog))
}
}
n := len(pp.sudogcache)
s := pp.sudogcache[n-1]
pp.sudogcache[n-1] = nil
pp.sudogcache = pp.sudogcache[:n-1]
if s.elem != nil {
throw("acquireSudog: found s.elem != nil in cache")
}
releasem(mp)
return s
}
//go:nosplit
func releaseSudog(s *sudog) {
if s.elem != nil {
throw("runtime: sudog with non-nil elem")
}
if s.isSelect {
throw("runtime: sudog with non-false isSelect")
}
if s.next != nil {
throw("runtime: sudog with non-nil next")
}
if s.prev != nil {
throw("runtime: sudog with non-nil prev")
}
if s.waitlink != nil {
throw("runtime: sudog with non-nil waitlink")
}
if s.c != nil {
throw("runtime: sudog with non-nil c")
}
gp := getg()
if gp.param != nil {
throw("runtime: releaseSudog with non-nil gp.param")
}
mp := acquirem() // avoid rescheduling to another P
pp := mp.p.ptr()
if len(pp.sudogcache) == cap(pp.sudogcache) {
// Transfer half of local cache to the central cache.
var first, last *sudog
for len(pp.sudogcache) > cap(pp.sudogcache)/2 {
n := len(pp.sudogcache)
p := pp.sudogcache[n-1]
pp.sudogcache[n-1] = nil
pp.sudogcache = pp.sudogcache[:n-1]
if first == nil {
first = p
} else {
last.next = p
}
last = p
}
lock(&sched.sudoglock)
last.next = sched.sudogcache
sched.sudogcache = first
unlock(&sched.sudoglock)
}
pp.sudogcache = append(pp.sudogcache, s)
releasem(mp)
}
// called from assembly.
func badmcall(fn func(*g)) {
throw("runtime: mcall called on m->g0 stack")
}
func badmcall2(fn func(*g)) {
throw("runtime: mcall function returned")
}
func badreflectcall() {
panic(plainError("arg size to reflect.call more than 1GB"))
}
//go:nosplit
//go:nowritebarrierrec
func badmorestackg0() {
if !crashStackImplemented {
writeErrStr("fatal: morestack on g0\n")
return
}
g := getg()
switchToCrashStack(func() {
print("runtime: morestack on g0, stack [", hex(g.stack.lo), " ", hex(g.stack.hi), "], sp=", hex(g.sched.sp), ", called from\n")
g.m.traceback = 2 // include pc and sp in stack trace
traceback1(g.sched.pc, g.sched.sp, g.sched.lr, g, 0)
print("\n")
throw("morestack on g0")
})
}
//go:nosplit
//go:nowritebarrierrec
func badmorestackgsignal() {
writeErrStr("fatal: morestack on gsignal\n")
}
//go:nosplit
func badctxt() {
throw("ctxt != 0")
}
// gcrash is a fake g that can be used when crashing due to bad
// stack conditions.
var gcrash g
var crashingG atomic.Pointer[g]
// Switch to crashstack and call fn, with special handling of
// concurrent and recursive cases.
//
// Nosplit as it is called in a bad stack condition (we know
// morestack would fail).
//
//go:nosplit
//go:nowritebarrierrec
func switchToCrashStack(fn func()) {
me := getg()
if crashingG.CompareAndSwapNoWB(nil, me) {
switchToCrashStack0(fn) // should never return
abort()
}
if crashingG.Load() == me {
// recursive crashing. too bad.
writeErrStr("fatal: recursive switchToCrashStack\n")
abort()
}
// Another g is crashing. Give it some time, hopefully it will finish traceback.
usleep_no_g(100)
writeErrStr("fatal: concurrent switchToCrashStack\n")
abort()
}
// Disable crash stack on Windows for now. Apparently, throwing an exception
// on a non-system-allocated crash stack causes EXCEPTION_STACK_OVERFLOW and
// hangs the process (see issue 63938).
const crashStackImplemented = (GOARCH == "amd64" || GOARCH == "arm64" || GOARCH == "mips64" || GOARCH == "mips64le" || GOARCH == "ppc64" || GOARCH == "ppc64le" || GOARCH == "riscv64" || GOARCH == "wasm") && GOOS != "windows"
//go:noescape
func switchToCrashStack0(fn func()) // in assembly
func lockedOSThread() bool {
gp := getg()
return gp.lockedm != 0 && gp.m.lockedg != 0
}
var (
// allgs contains all Gs ever created (including dead Gs), and thus
// never shrinks.
//
// Access via the slice is protected by allglock or stop-the-world.
// Readers that cannot take the lock may (carefully!) use the atomic
// variables below.
allglock mutex
allgs []*g
// allglen and allgptr are atomic variables that contain len(allgs) and
// &allgs[0] respectively. Proper ordering depends on totally-ordered
// loads and stores. Writes are protected by allglock.
//
// allgptr is updated before allglen. Readers should read allglen
// before allgptr to ensure that allglen is always <= len(allgptr). New
// Gs appended during the race can be missed. For a consistent view of
// all Gs, allglock must be held.
//
// allgptr copies should always be stored as a concrete type or
// unsafe.Pointer, not uintptr, to ensure that GC can still reach it
// even if it points to a stale array.
allglen uintptr
allgptr **g
)
func allgadd(gp *g) {
if readgstatus(gp) == _Gidle {
throw("allgadd: bad status Gidle")
}
lock(&allglock)
allgs = append(allgs, gp)
if &allgs[0] != allgptr {
atomicstorep(unsafe.Pointer(&allgptr), unsafe.Pointer(&allgs[0]))
}
atomic.Storeuintptr(&allglen, uintptr(len(allgs)))
unlock(&allglock)
}
// allGsSnapshot returns a snapshot of the slice of all Gs.
//
// The world must be stopped or allglock must be held.
func allGsSnapshot() []*g {
assertWorldStoppedOrLockHeld(&allglock)
// Because the world is stopped or allglock is held, allgadd
// cannot happen concurrently with this. allgs grows
// monotonically and existing entries never change, so we can
// simply return a copy of the slice header. For added safety,
// we trim everything past len because that can still change.
return allgs[:len(allgs):len(allgs)]
}
// atomicAllG returns &allgs[0] and len(allgs) for use with atomicAllGIndex.
func atomicAllG() (**g, uintptr) {
length := atomic.Loaduintptr(&allglen)
ptr := (**g)(atomic.Loadp(unsafe.Pointer(&allgptr)))
return ptr, length
}
// atomicAllGIndex returns ptr[i] with the allgptr returned from atomicAllG.
func atomicAllGIndex(ptr **g, i uintptr) *g {
return *(**g)(add(unsafe.Pointer(ptr), i*goarch.PtrSize))
}
// forEachG calls fn on every G from allgs.
//
// forEachG takes a lock to exclude concurrent addition of new Gs.
func forEachG(fn func(gp *g)) {
lock(&allglock)
for _, gp := range allgs {
fn(gp)
}
unlock(&allglock)
}
// forEachGRace calls fn on every G from allgs.
//
// forEachGRace avoids locking, but does not exclude addition of new Gs during
// execution, which may be missed.
func forEachGRace(fn func(gp *g)) {
ptr, length := atomicAllG()
for i := uintptr(0); i < length; i++ {
gp := atomicAllGIndex(ptr, i)
fn(gp)
}
return
}
const (
// Number of goroutine ids to grab from sched.goidgen to local per-P cache at once.
// 16 seems to provide enough amortization, but other than that it's mostly arbitrary number.
_GoidCacheBatch = 16
)
// cpuinit sets up CPU feature flags and calls internal/cpu.Initialize. env should be the complete
// value of the GODEBUG environment variable.
func cpuinit(env string) {
switch GOOS {
case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux":
cpu.DebugOptions = true
}
cpu.Initialize(env)
// Support cpu feature variables are used in code generated by the compiler
// to guard execution of instructions that can not be assumed to be always supported.
switch GOARCH {
case "386", "amd64":
x86HasPOPCNT = cpu.X86.HasPOPCNT
x86HasSSE41 = cpu.X86.HasSSE41
x86HasFMA = cpu.X86.HasFMA
case "arm":
armHasVFPv4 = cpu.ARM.HasVFPv4
case "arm64":
arm64HasATOMICS = cpu.ARM64.HasATOMICS
}
}
// getGodebugEarly extracts the environment variable GODEBUG from the environment on
// Unix-like operating systems and returns it. This function exists to extract GODEBUG
// early before much of the runtime is initialized.
func getGodebugEarly() string {
const prefix = "GODEBUG="
var env string
switch GOOS {
case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux":
// Similar to goenv_unix but extracts the environment value for
// GODEBUG directly.
// TODO(moehrmann): remove when general goenvs() can be called before cpuinit()
n := int32(0)
for argv_index(argv, argc+1+n) != nil {
n++
}
for i := int32(0); i < n; i++ {
p := argv_index(argv, argc+1+i)
s := unsafe.String(p, findnull(p))
if hasPrefix(s, prefix) {
env = gostring(p)[len(prefix):]
break
}
}
}
return env
}
// The bootstrap sequence is:
//
// call osinit
// call schedinit
// make & queue new G
// call runtime·mstart
//
// The new G calls runtime·main.
func schedinit() {
lockInit(&sched.lock, lockRankSched)
lockInit(&sched.sysmonlock, lockRankSysmon)
lockInit(&sched.deferlock, lockRankDefer)
lockInit(&sched.sudoglock, lockRankSudog)
lockInit(&deadlock, lockRankDeadlock)
lockInit(&paniclk, lockRankPanic)
lockInit(&allglock, lockRankAllg)
lockInit(&allpLock, lockRankAllp)
lockInit(&reflectOffs.lock, lockRankReflectOffs)
lockInit(&finlock, lockRankFin)
lockInit(&cpuprof.lock, lockRankCpuprof)
allocmLock.init(lockRankAllocmR, lockRankAllocmRInternal, lockRankAllocmW)
execLock.init(lockRankExecR, lockRankExecRInternal, lockRankExecW)
traceLockInit()
// Enforce that this lock is always a leaf lock.
// All of this lock's critical sections should be
// extremely short.
lockInit(&memstats.heapStats.noPLock, lockRankLeafRank)
// raceinit must be the first call to race detector.
// In particular, it must be done before mallocinit below calls racemapshadow.
gp := getg()
if raceenabled {
gp.racectx, raceprocctx0 = raceinit()
}
sched.maxmcount = 10000
// The world starts stopped.
worldStopped()
ticks.init() // run as early as possible
moduledataverify()
stackinit()
mallocinit()
godebug := getGodebugEarly()
initPageTrace(godebug) // must run after mallocinit but before anything allocates
cpuinit(godebug) // must run before alginit
randinit() // must run before alginit, mcommoninit
alginit() // maps, hash, rand must not be used before this call
mcommoninit(gp.m, -1)
modulesinit() // provides activeModules
typelinksinit() // uses maps, activeModules
itabsinit() // uses activeModules
stkobjinit() // must run before GC starts
sigsave(&gp.m.sigmask)
initSigmask = gp.m.sigmask
goargs()
goenvs()
secure()
checkfds()
parsedebugvars()
gcinit()
// Allocate stack space that can be used when crashing due to bad stack
// conditions, e.g. morestack on g0.
gcrash.stack = stackalloc(16384)
gcrash.stackguard0 = gcrash.stack.lo + 1000
gcrash.stackguard1 = gcrash.stack.lo + 1000
// if disableMemoryProfiling is set, update MemProfileRate to 0 to turn off memprofile.
// Note: parsedebugvars may update MemProfileRate, but when disableMemoryProfiling is
// set to true by the linker, it means that nothing is consuming the profile, it is
// safe to set MemProfileRate to 0.
if disableMemoryProfiling {
MemProfileRate = 0
}
lock(&sched.lock)
sched.lastpoll.Store(nanotime())
procs := ncpu
if n, ok := atoi32(gogetenv("GOMAXPROCS")); ok && n > 0 {
procs = n
}
if procresize(procs) != nil {
throw("unknown runnable goroutine during bootstrap")
}
unlock(&sched.lock)
// World is effectively started now, as P's can run.
worldStarted()
if buildVersion == "" {
// Condition should never trigger. This code just serves
// to ensure runtime·buildVersion is kept in the resulting binary.
buildVersion = "unknown"
}
if len(modinfo) == 1 {
// Condition should never trigger. This code just serves
// to ensure runtime·modinfo is kept in the resulting binary.
modinfo = ""
}
}
func dumpgstatus(gp *g) {
thisg := getg()
print("runtime: gp: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n")
print("runtime: getg: g=", thisg, ", goid=", thisg.goid, ", g->atomicstatus=", readgstatus(thisg), "\n")
}
// sched.lock must be held.
func checkmcount() {
assertLockHeld(&sched.lock)
// Exclude extra M's, which are used for cgocallback from threads
// created in C.
//
// The purpose of the SetMaxThreads limit is to avoid accidental fork
// bomb from something like millions of goroutines blocking on system
// calls, causing the runtime to create millions of threads. By
// definition, this isn't a problem for threads created in C, so we
// exclude them from the limit. See https://go.dev/issue/60004.
count := mcount() - int32(extraMInUse.Load()) - int32(extraMLength.Load())
if count > sched.maxmcount {
print("runtime: program exceeds ", sched.maxmcount, "-thread limit\n")
throw("thread exhaustion")
}
}
// mReserveID returns the next ID to use for a new m. This new m is immediately
// considered 'running' by checkdead.
//
// sched.lock must be held.
func mReserveID() int64 {
assertLockHeld(&sched.lock)
if sched.mnext+1 < sched.mnext {
throw("runtime: thread ID overflow")
}
id := sched.mnext
sched.mnext++
checkmcount()
return id
}
// Pre-allocated ID may be passed as 'id', or omitted by passing -1.
func mcommoninit(mp *m, id int64) {
gp := getg()
// g0 stack won't make sense for user (and is not necessary unwindable).
if gp != gp.m.g0 {
callers(1, mp.createstack[:])
}
lock(&sched.lock)
if id >= 0 {
mp.id = id
} else {
mp.id = mReserveID()
}
mrandinit(mp)
mpreinit(mp)
if mp.gsignal != nil {
mp.gsignal.stackguard1 = mp.gsignal.stack.lo + stackGuard
}
// Add to allm so garbage collector doesn't free g->m
// when it is just in a register or thread-local storage.
mp.alllink = allm
// NumCgoCall() and others iterate over allm w/o schedlock,
// so we need to publish it safely.
atomicstorep(unsafe.Pointer(&allm), unsafe.Pointer(mp))
unlock(&sched.lock)
// Allocate memory to hold a cgo traceback if the cgo call crashes.
if iscgo || GOOS == "solaris" || GOOS == "illumos" || GOOS == "windows" {
mp.cgoCallers = new(cgoCallers)
}
}
func (mp *m) becomeSpinning() {
mp.spinning = true
sched.nmspinning.Add(1)
sched.needspinning.Store(0)
}
func (mp *m) hasCgoOnStack() bool {
return mp.ncgo > 0 || mp.isextra
}
const (
// osHasLowResTimer indicates that the platform's internal timer system has a low resolution,
// typically on the order of 1 ms or more.
osHasLowResTimer = GOOS == "windows" || GOOS == "openbsd" || GOOS == "netbsd"
// osHasLowResClockInt is osHasLowResClock but in integer form, so it can be used to create
// constants conditionally.
osHasLowResClockInt = goos.IsWindows
// osHasLowResClock indicates that timestamps produced by nanotime on the platform have a
// low resolution, typically on the order of 1 ms or more.
osHasLowResClock = osHasLowResClockInt > 0
)
// Mark gp ready to run.
func ready(gp *g, traceskip int, next bool) {
status := readgstatus(gp)
// Mark runnable.
mp := acquirem() // disable preemption because it can be holding p in a local var
if status&^_Gscan != _Gwaiting {
dumpgstatus(gp)
throw("bad g->status in ready")
}
// status is Gwaiting or Gscanwaiting, make Grunnable and put on runq
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, traceskip)
traceRelease(trace)
}
runqput(mp.p.ptr(), gp, next)
wakep()
releasem(mp)
}
// freezeStopWait is a large value that freezetheworld sets
// sched.stopwait to in order to request that all Gs permanently stop.
const freezeStopWait = 0x7fffffff
// freezing is set to non-zero if the runtime is trying to freeze the
// world.
var freezing atomic.Bool
// Similar to stopTheWorld but best-effort and can be called several times.
// There is no reverse operation, used during crashing.
// This function must not lock any mutexes.
func freezetheworld() {
freezing.Store(true)
if debug.dontfreezetheworld > 0 {
// Don't prempt Ps to stop goroutines. That will perturb
// scheduler state, making debugging more difficult. Instead,
// allow goroutines to continue execution.
//
// fatalpanic will tracebackothers to trace all goroutines. It
// is unsafe to trace a running goroutine, so tracebackothers
// will skip running goroutines. That is OK and expected, we
// expect users of dontfreezetheworld to use core files anyway.
//
// However, allowing the scheduler to continue running free
// introduces a race: a goroutine may be stopped when
// tracebackothers checks its status, and then start running
// later when we are in the middle of traceback, potentially
// causing a crash.
//
// To mitigate this, when an M naturally enters the scheduler,
// schedule checks if freezing is set and if so stops
// execution. This guarantees that while Gs can transition from
// running to stopped, they can never transition from stopped
// to running.
//
// The sleep here allows racing Ms that missed freezing and are
// about to run a G to complete the transition to running
// before we start traceback.
usleep(1000)
return
}
// stopwait and preemption requests can be lost
// due to races with concurrently executing threads,
// so try several times
for i := 0; i < 5; i++ {
// this should tell the scheduler to not start any new goroutines
sched.stopwait = freezeStopWait
sched.gcwaiting.Store(true)
// this should stop running goroutines
if !preemptall() {
break // no running goroutines
}
usleep(1000)
}
// to be sure
usleep(1000)
preemptall()
usleep(1000)
}
// All reads and writes of g's status go through readgstatus, casgstatus
// castogscanstatus, casfrom_Gscanstatus.
//
//go:nosplit
func readgstatus(gp *g) uint32 {
return gp.atomicstatus.Load()
}
// The Gscanstatuses are acting like locks and this releases them.
// If it proves to be a performance hit we should be able to make these
// simple atomic stores but for now we are going to throw if
// we see an inconsistent state.
func casfrom_Gscanstatus(gp *g, oldval, newval uint32) {
success := false
// Check that transition is valid.
switch oldval {
default:
print("runtime: casfrom_Gscanstatus bad oldval gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n")
dumpgstatus(gp)
throw("casfrom_Gscanstatus:top gp->status is not in scan state")
case _Gscanrunnable,
_Gscanwaiting,
_Gscanrunning,
_Gscansyscall,
_Gscanpreempted:
if newval == oldval&^_Gscan {
success = gp.atomicstatus.CompareAndSwap(oldval, newval)
}
}
if !success {
print("runtime: casfrom_Gscanstatus failed gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n")
dumpgstatus(gp)
throw("casfrom_Gscanstatus: gp->status is not in scan state")
}
releaseLockRank(lockRankGscan)
}
// This will return false if the gp is not in the expected status and the cas fails.
// This acts like a lock acquire while the casfromgstatus acts like a lock release.
func castogscanstatus(gp *g, oldval, newval uint32) bool {
switch oldval {
case _Grunnable,
_Grunning,
_Gwaiting,
_Gsyscall:
if newval == oldval|_Gscan {
r := gp.atomicstatus.CompareAndSwap(oldval, newval)
if r {
acquireLockRank(lockRankGscan)
}
return r
}
}
print("runtime: castogscanstatus oldval=", hex(oldval), " newval=", hex(newval), "\n")
throw("castogscanstatus")
panic("not reached")
}
// casgstatusAlwaysTrack is a debug flag that causes casgstatus to always track
// various latencies on every transition instead of sampling them.
var casgstatusAlwaysTrack = false
// If asked to move to or from a Gscanstatus this will throw. Use the castogscanstatus
// and casfrom_Gscanstatus instead.
// casgstatus will loop if the g->atomicstatus is in a Gscan status until the routine that
// put it in the Gscan state is finished.
//
//go:nosplit
func casgstatus(gp *g, oldval, newval uint32) {
if (oldval&_Gscan != 0) || (newval&_Gscan != 0) || oldval == newval {
systemstack(func() {
print("runtime: casgstatus: oldval=", hex(oldval), " newval=", hex(newval), "\n")
throw("casgstatus: bad incoming values")
})
}
acquireLockRank(lockRankGscan)
releaseLockRank(lockRankGscan)
// See https://golang.org/cl/21503 for justification of the yield delay.
const yieldDelay = 5 * 1000
var nextYield int64
// loop if gp->atomicstatus is in a scan state giving
// GC time to finish and change the state to oldval.
for i := 0; !gp.atomicstatus.CompareAndSwap(oldval, newval); i++ {
if oldval == _Gwaiting && gp.atomicstatus.Load() == _Grunnable {
throw("casgstatus: waiting for Gwaiting but is Grunnable")
}
if i == 0 {
nextYield = nanotime() + yieldDelay
}
if nanotime() < nextYield {
for x := 0; x < 10 && gp.atomicstatus.Load() != oldval; x++ {
procyield(1)
}
} else {
osyield()
nextYield = nanotime() + yieldDelay/2
}
}
if oldval == _Grunning {
// Track every gTrackingPeriod time a goroutine transitions out of running.
if casgstatusAlwaysTrack || gp.trackingSeq%gTrackingPeriod == 0 {
gp.tracking = true
}
gp.trackingSeq++
}
if !gp.tracking {
return
}
// Handle various kinds of tracking.
//
// Currently:
// - Time spent in runnable.
// - Time spent blocked on a sync.Mutex or sync.RWMutex.
switch oldval {
case _Grunnable:
// We transitioned out of runnable, so measure how much
// time we spent in this state and add it to
// runnableTime.
now := nanotime()
gp.runnableTime += now - gp.trackingStamp
gp.trackingStamp = 0
case _Gwaiting:
if !gp.waitreason.isMutexWait() {
// Not blocking on a lock.
break
}
// Blocking on a lock, measure it. Note that because we're
// sampling, we have to multiply by our sampling period to get
// a more representative estimate of the absolute value.
// gTrackingPeriod also represents an accurate sampling period
// because we can only enter this state from _Grunning.
now := nanotime()
sched.totalMutexWaitTime.Add((now - gp.trackingStamp) * gTrackingPeriod)
gp.trackingStamp = 0
}
switch newval {
case _Gwaiting:
if !gp.waitreason.isMutexWait() {
// Not blocking on a lock.
break
}
// Blocking on a lock. Write down the timestamp.
now := nanotime()
gp.trackingStamp = now
case _Grunnable:
// We just transitioned into runnable, so record what
// time that happened.
now := nanotime()
gp.trackingStamp = now
case _Grunning:
// We're transitioning into running, so turn off
// tracking and record how much time we spent in
// runnable.
gp.tracking = false
sched.timeToRun.record(gp.runnableTime)
gp.runnableTime = 0
}
}
// casGToWaiting transitions gp from old to _Gwaiting, and sets the wait reason.
//
// Use this over casgstatus when possible to ensure that a waitreason is set.
func casGToWaiting(gp *g, old uint32, reason waitReason) {
// Set the wait reason before calling casgstatus, because casgstatus will use it.
gp.waitreason = reason
casgstatus(gp, old, _Gwaiting)
}
// casgstatus(gp, oldstatus, Gcopystack), assuming oldstatus is Gwaiting or Grunnable.
// Returns old status. Cannot call casgstatus directly, because we are racing with an
// async wakeup that might come in from netpoll. If we see Gwaiting from the readgstatus,
// it might have become Grunnable by the time we get to the cas. If we called casgstatus,
// it would loop waiting for the status to go back to Gwaiting, which it never will.
//
//go:nosplit
func casgcopystack(gp *g) uint32 {
for {
oldstatus := readgstatus(gp) &^ _Gscan
if oldstatus != _Gwaiting && oldstatus != _Grunnable {
throw("copystack: bad status, not Gwaiting or Grunnable")
}
if gp.atomicstatus.CompareAndSwap(oldstatus, _Gcopystack) {
return oldstatus
}
}
}
// casGToPreemptScan transitions gp from _Grunning to _Gscan|_Gpreempted.
//
// TODO(austin): This is the only status operation that both changes
// the status and locks the _Gscan bit. Rethink this.
func casGToPreemptScan(gp *g, old, new uint32) {
if old != _Grunning || new != _Gscan|_Gpreempted {
throw("bad g transition")
}
acquireLockRank(lockRankGscan)
for !gp.atomicstatus.CompareAndSwap(_Grunning, _Gscan|_Gpreempted) {
}
}
// casGFromPreempted attempts to transition gp from _Gpreempted to
// _Gwaiting. If successful, the caller is responsible for
// re-scheduling gp.
func casGFromPreempted(gp *g, old, new uint32) bool {
if old != _Gpreempted || new != _Gwaiting {
throw("bad g transition")
}
gp.waitreason = waitReasonPreempted
return gp.atomicstatus.CompareAndSwap(_Gpreempted, _Gwaiting)
}
// stwReason is an enumeration of reasons the world is stopping.
type stwReason uint8
// Reasons to stop-the-world.
//
// Avoid reusing reasons and add new ones instead.
const (
stwUnknown stwReason = iota // "unknown"
stwGCMarkTerm // "GC mark termination"
stwGCSweepTerm // "GC sweep termination"
stwWriteHeapDump // "write heap dump"
stwGoroutineProfile // "goroutine profile"
stwGoroutineProfileCleanup // "goroutine profile cleanup"
stwAllGoroutinesStack // "all goroutines stack trace"
stwReadMemStats // "read mem stats"
stwAllThreadsSyscall // "AllThreadsSyscall"
stwGOMAXPROCS // "GOMAXPROCS"
stwStartTrace // "start trace"
stwStopTrace // "stop trace"
stwForTestCountPagesInUse // "CountPagesInUse (test)"
stwForTestReadMetricsSlow // "ReadMetricsSlow (test)"
stwForTestReadMemStatsSlow // "ReadMemStatsSlow (test)"
stwForTestPageCachePagesLeaked // "PageCachePagesLeaked (test)"
stwForTestResetDebugLog // "ResetDebugLog (test)"
)
func (r stwReason) String() string {
return stwReasonStrings[r]
}
func (r stwReason) isGC() bool {
return r == stwGCMarkTerm || r == stwGCSweepTerm
}
// If you add to this list, also add it to src/internal/trace/parser.go.
// If you change the values of any of the stw* constants, bump the trace
// version number and make a copy of this.
var stwReasonStrings = [...]string{
stwUnknown: "unknown",
stwGCMarkTerm: "GC mark termination",
stwGCSweepTerm: "GC sweep termination",
stwWriteHeapDump: "write heap dump",
stwGoroutineProfile: "goroutine profile",
stwGoroutineProfileCleanup: "goroutine profile cleanup",
stwAllGoroutinesStack: "all goroutines stack trace",
stwReadMemStats: "read mem stats",
stwAllThreadsSyscall: "AllThreadsSyscall",
stwGOMAXPROCS: "GOMAXPROCS",
stwStartTrace: "start trace",
stwStopTrace: "stop trace",
stwForTestCountPagesInUse: "CountPagesInUse (test)",
stwForTestReadMetricsSlow: "ReadMetricsSlow (test)",
stwForTestReadMemStatsSlow: "ReadMemStatsSlow (test)",
stwForTestPageCachePagesLeaked: "PageCachePagesLeaked (test)",
stwForTestResetDebugLog: "ResetDebugLog (test)",
}
// worldStop provides context from the stop-the-world required by the
// start-the-world.
type worldStop struct {
reason stwReason
start int64
}
// Temporary variable for stopTheWorld, when it can't write to the stack.
//
// Protected by worldsema.
var stopTheWorldContext worldStop
// stopTheWorld stops all P's from executing goroutines, interrupting
// all goroutines at GC safe points and records reason as the reason
// for the stop. On return, only the current goroutine's P is running.
// stopTheWorld must not be called from a system stack and the caller
// must not hold worldsema. The caller must call startTheWorld when
// other P's should resume execution.
//
// stopTheWorld is safe for multiple goroutines to call at the
// same time. Each will execute its own stop, and the stops will
// be serialized.
//
// This is also used by routines that do stack dumps. If the system is
// in panic or being exited, this may not reliably stop all
// goroutines.
//
// Returns the STW context. When starting the world, this context must be
// passed to startTheWorld.
func stopTheWorld(reason stwReason) worldStop {
semacquire(&worldsema)
gp := getg()
gp.m.preemptoff = reason.String()
systemstack(func() {
// Mark the goroutine which called stopTheWorld preemptible so its
// stack may be scanned.
// This lets a mark worker scan us while we try to stop the world
// since otherwise we could get in a mutual preemption deadlock.
// We must not modify anything on the G stack because a stack shrink
// may occur. A stack shrink is otherwise OK though because in order
// to return from this function (and to leave the system stack) we
// must have preempted all goroutines, including any attempting
// to scan our stack, in which case, any stack shrinking will
// have already completed by the time we exit.
//
// N.B. The execution tracer is not aware of this status
// transition and handles it specially based on the
// wait reason.
casGToWaiting(gp, _Grunning, waitReasonStoppingTheWorld)
stopTheWorldContext = stopTheWorldWithSema(reason) // avoid write to stack
casgstatus(gp, _Gwaiting, _Grunning)
})
return stopTheWorldContext
}
// startTheWorld undoes the effects of stopTheWorld.
//
// w must be the worldStop returned by stopTheWorld.
func startTheWorld(w worldStop) {
systemstack(func() { startTheWorldWithSema(0, w) })
// worldsema must be held over startTheWorldWithSema to ensure
// gomaxprocs cannot change while worldsema is held.
//
// Release worldsema with direct handoff to the next waiter, but
// acquirem so that semrelease1 doesn't try to yield our time.
//
// Otherwise if e.g. ReadMemStats is being called in a loop,
// it might stomp on other attempts to stop the world, such as
// for starting or ending GC. The operation this blocks is
// so heavy-weight that we should just try to be as fair as
// possible here.
//
// We don't want to just allow us to get preempted between now
// and releasing the semaphore because then we keep everyone
// (including, for example, GCs) waiting longer.
mp := acquirem()
mp.preemptoff = ""
semrelease1(&worldsema, true, 0)
releasem(mp)
}
// stopTheWorldGC has the same effect as stopTheWorld, but blocks
// until the GC is not running. It also blocks a GC from starting
// until startTheWorldGC is called.
func stopTheWorldGC(reason stwReason) worldStop {
semacquire(&gcsema)
return stopTheWorld(reason)
}
// startTheWorldGC undoes the effects of stopTheWorldGC.
//
// w must be the worldStop returned by stopTheWorld.
func startTheWorldGC(w worldStop) {
startTheWorld(w)
semrelease(&gcsema)
}
// Holding worldsema grants an M the right to try to stop the world.
var worldsema uint32 = 1
// Holding gcsema grants the M the right to block a GC, and blocks
// until the current GC is done. In particular, it prevents gomaxprocs
// from changing concurrently.
//
// TODO(mknyszek): Once gomaxprocs and the execution tracer can handle
// being changed/enabled during a GC, remove this.
var gcsema uint32 = 1
// stopTheWorldWithSema is the core implementation of stopTheWorld.
// The caller is responsible for acquiring worldsema and disabling
// preemption first and then should stopTheWorldWithSema on the system
// stack:
//
// semacquire(&worldsema, 0)
// m.preemptoff = "reason"
// var stw worldStop
// systemstack(func() {
// stw = stopTheWorldWithSema(reason)
// })
//
// When finished, the caller must either call startTheWorld or undo
// these three operations separately:
//
// m.preemptoff = ""
// systemstack(func() {
// now = startTheWorldWithSema(stw)
// })
// semrelease(&worldsema)
//
// It is allowed to acquire worldsema once and then execute multiple
// startTheWorldWithSema/stopTheWorldWithSema pairs.
// Other P's are able to execute between successive calls to
// startTheWorldWithSema and stopTheWorldWithSema.
// Holding worldsema causes any other goroutines invoking
// stopTheWorld to block.
//
// Returns the STW context. When starting the world, this context must be
// passed to startTheWorldWithSema.
func stopTheWorldWithSema(reason stwReason) worldStop {
trace := traceAcquire()
if trace.ok() {
trace.STWStart(reason)
traceRelease(trace)
}
gp := getg()
// If we hold a lock, then we won't be able to stop another M
// that is blocked trying to acquire the lock.
if gp.m.locks > 0 {
throw("stopTheWorld: holding locks")
}
lock(&sched.lock)
start := nanotime() // exclude time waiting for sched.lock from start and total time metrics.
sched.stopwait = gomaxprocs
sched.gcwaiting.Store(true)
preemptall()
// stop current P
gp.m.p.ptr().status = _Pgcstop // Pgcstop is only diagnostic.
sched.stopwait--
// try to retake all P's in Psyscall status
trace = traceAcquire()
for _, pp := range allp {
s := pp.status
if s == _Psyscall && atomic.Cas(&pp.status, s, _Pgcstop) {
if trace.ok() {
trace.GoSysBlock(pp)
trace.ProcSteal(pp, false)
}
pp.syscalltick++
sched.stopwait--
}
}
if trace.ok() {
traceRelease(trace)
}
// stop idle P's
now := nanotime()
for {
pp, _ := pidleget(now)
if pp == nil {
break
}
pp.status = _Pgcstop
sched.stopwait--
}
wait := sched.stopwait > 0
unlock(&sched.lock)
// wait for remaining P's to stop voluntarily
if wait {
for {
// wait for 100us, then try to re-preempt in case of any races
if notetsleep(&sched.stopnote, 100*1000) {
noteclear(&sched.stopnote)
break
}
preemptall()
}
}
startTime := nanotime() - start
if reason.isGC() {
sched.stwStoppingTimeGC.record(startTime)
} else {
sched.stwStoppingTimeOther.record(startTime)
}
// sanity checks
bad := ""
if sched.stopwait != 0 {
bad = "stopTheWorld: not stopped (stopwait != 0)"
} else {
for _, pp := range allp {
if pp.status != _Pgcstop {
bad = "stopTheWorld: not stopped (status != _Pgcstop)"
}
}
}
if freezing.Load() {
// Some other thread is panicking. This can cause the
// sanity checks above to fail if the panic happens in
// the signal handler on a stopped thread. Either way,
// we should halt this thread.
lock(&deadlock)
lock(&deadlock)
}
if bad != "" {
throw(bad)
}
worldStopped()
return worldStop{reason: reason, start: start}
}
// reason is the same STW reason passed to stopTheWorld. start is the start
// time returned by stopTheWorld.
//
// now is the current time; prefer to pass 0 to capture a fresh timestamp.
//
// stattTheWorldWithSema returns now.
func startTheWorldWithSema(now int64, w worldStop) int64 {
assertWorldStopped()
mp := acquirem() // disable preemption because it can be holding p in a local var
if netpollinited() {
list, delta := netpoll(0) // non-blocking
injectglist(&list)
netpollAdjustWaiters(delta)
}
lock(&sched.lock)
procs := gomaxprocs
if newprocs != 0 {
procs = newprocs
newprocs = 0
}
p1 := procresize(procs)
sched.gcwaiting.Store(false)
if sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
worldStarted()
for p1 != nil {
p := p1
p1 = p1.link.ptr()
if p.m != 0 {
mp := p.m.ptr()
p.m = 0
if mp.nextp != 0 {
throw("startTheWorld: inconsistent mp->nextp")
}
mp.nextp.set(p)
notewakeup(&mp.park)
} else {
// Start M to run P. Do not start another M below.
newm(nil, p, -1)
}
}
// Capture start-the-world time before doing clean-up tasks.
if now == 0 {
now = nanotime()
}
totalTime := now - w.start
if w.reason.isGC() {
sched.stwTotalTimeGC.record(totalTime)
} else {
sched.stwTotalTimeOther.record(totalTime)
}
trace := traceAcquire()
if trace.ok() {
trace.STWDone()
traceRelease(trace)
}
// Wakeup an additional proc in case we have excessive runnable goroutines
// in local queues or in the global queue. If we don't, the proc will park itself.
// If we have lots of excessive work, resetspinning will unpark additional procs as necessary.
wakep()
releasem(mp)
return now
}
// usesLibcall indicates whether this runtime performs system calls
// via libcall.
func usesLibcall() bool {
switch GOOS {
case "aix", "darwin", "illumos", "ios", "solaris", "windows":
return true
case "openbsd":
return GOARCH != "mips64"
}
return false
}
// mStackIsSystemAllocated indicates whether this runtime starts on a
// system-allocated stack.
func mStackIsSystemAllocated() bool {
switch GOOS {
case "aix", "darwin", "plan9", "illumos", "ios", "solaris", "windows":
return true
case "openbsd":
return GOARCH != "mips64"
}
return false
}
// mstart is the entry-point for new Ms.
// It is written in assembly, uses ABI0, is marked TOPFRAME, and calls mstart0.
func mstart()
// mstart0 is the Go entry-point for new Ms.
// This must not split the stack because we may not even have stack
// bounds set up yet.
//
// May run during STW (because it doesn't have a P yet), so write
// barriers are not allowed.
//
//go:nosplit
//go:nowritebarrierrec
func mstart0() {
gp := getg()
osStack := gp.stack.lo == 0
if osStack {
// Initialize stack bounds from system stack.
// Cgo may have left stack size in stack.hi.
// minit may update the stack bounds.
//
// Note: these bounds may not be very accurate.
// We set hi to &size, but there are things above
// it. The 1024 is supposed to compensate this,
// but is somewhat arbitrary.
size := gp.stack.hi
if size == 0 {
size = 16384 * sys.StackGuardMultiplier
}
gp.stack.hi = uintptr(noescape(unsafe.Pointer(&size)))
gp.stack.lo = gp.stack.hi - size + 1024
}
// Initialize stack guard so that we can start calling regular
// Go code.
gp.stackguard0 = gp.stack.lo + stackGuard
// This is the g0, so we can also call go:systemstack
// functions, which check stackguard1.
gp.stackguard1 = gp.stackguard0
mstart1()
// Exit this thread.
if mStackIsSystemAllocated() {
// Windows, Solaris, illumos, Darwin, AIX and Plan 9 always system-allocate
// the stack, but put it in gp.stack before mstart,
// so the logic above hasn't set osStack yet.
osStack = true
}
mexit(osStack)
}
// The go:noinline is to guarantee the getcallerpc/getcallersp below are safe,
// so that we can set up g0.sched to return to the call of mstart1 above.
//
//go:noinline
func mstart1() {
gp := getg()
if gp != gp.m.g0 {
throw("bad runtime·mstart")
}
// Set up m.g0.sched as a label returning to just
// after the mstart1 call in mstart0 above, for use by goexit0 and mcall.
// We're never coming back to mstart1 after we call schedule,
// so other calls can reuse the current frame.
// And goexit0 does a gogo that needs to return from mstart1
// and let mstart0 exit the thread.
gp.sched.g = guintptr(unsafe.Pointer(gp))
gp.sched.pc = getcallerpc()
gp.sched.sp = getcallersp()
asminit()
minit()
// Install signal handlers; after minit so that minit can
// prepare the thread to be able to handle the signals.
if gp.m == &m0 {
mstartm0()
}
if fn := gp.m.mstartfn; fn != nil {
fn()
}
if gp.m != &m0 {
acquirep(gp.m.nextp.ptr())
gp.m.nextp = 0
}
schedule()
}
// mstartm0 implements part of mstart1 that only runs on the m0.
//
// Write barriers are allowed here because we know the GC can't be
// running yet, so they'll be no-ops.
//
//go:yeswritebarrierrec
func mstartm0() {
// Create an extra M for callbacks on threads not created by Go.
// An extra M is also needed on Windows for callbacks created by
// syscall.NewCallback. See issue #6751 for details.
if (iscgo || GOOS == "windows") && !cgoHasExtraM {
cgoHasExtraM = true
newextram()
}
initsig(false)
}
// mPark causes a thread to park itself, returning once woken.
//
//go:nosplit
func mPark() {
gp := getg()
notesleep(&gp.m.park)
noteclear(&gp.m.park)
}
// mexit tears down and exits the current thread.
//
// Don't call this directly to exit the thread, since it must run at
// the top of the thread stack. Instead, use gogo(&gp.m.g0.sched) to
// unwind the stack to the point that exits the thread.
//
// It is entered with m.p != nil, so write barriers are allowed. It
// will release the P before exiting.
//
//go:yeswritebarrierrec
func mexit(osStack bool) {
mp := getg().m
if mp == &m0 {
// This is the main thread. Just wedge it.
//
// On Linux, exiting the main thread puts the process
// into a non-waitable zombie state. On Plan 9,
// exiting the main thread unblocks wait even though
// other threads are still running. On Solaris we can
// neither exitThread nor return from mstart. Other
// bad things probably happen on other platforms.
//
// We could try to clean up this M more before wedging
// it, but that complicates signal handling.
handoffp(releasep())
lock(&sched.lock)
sched.nmfreed++
checkdead()
unlock(&sched.lock)
mPark()
throw("locked m0 woke up")
}
sigblock(true)
unminit()
// Free the gsignal stack.
if mp.gsignal != nil {
stackfree(mp.gsignal.stack)
// On some platforms, when calling into VDSO (e.g. nanotime)
// we store our g on the gsignal stack, if there is one.
// Now the stack is freed, unlink it from the m, so we
// won't write to it when calling VDSO code.
mp.gsignal = nil
}
// Remove m from allm.
lock(&sched.lock)
for pprev := &allm; *pprev != nil; pprev = &(*pprev).alllink {
if *pprev == mp {
*pprev = mp.alllink
goto found
}
}
throw("m not found in allm")
found:
// Events must not be traced after this point.
// Delay reaping m until it's done with the stack.
//
// Put mp on the free list, though it will not be reaped while freeWait
// is freeMWait. mp is no longer reachable via allm, so even if it is
// on an OS stack, we must keep a reference to mp alive so that the GC
// doesn't free mp while we are still using it.
//
// Note that the free list must not be linked through alllink because
// some functions walk allm without locking, so may be using alllink.
//
// N.B. It's important that the M appears on the free list simultaneously
// with it being removed so that the tracer can find it.
mp.freeWait.Store(freeMWait)
mp.freelink = sched.freem
sched.freem = mp
unlock(&sched.lock)
atomic.Xadd64(&ncgocall, int64(mp.ncgocall))
sched.totalRuntimeLockWaitTime.Add(mp.mLockProfile.waitTime.Load())
// Release the P.
handoffp(releasep())
// After this point we must not have write barriers.
// Invoke the deadlock detector. This must happen after
// handoffp because it may have started a new M to take our
// P's work.
lock(&sched.lock)
sched.nmfreed++
checkdead()
unlock(&sched.lock)
if GOOS == "darwin" || GOOS == "ios" {
// Make sure pendingPreemptSignals is correct when an M exits.
// For #41702.
if mp.signalPending.Load() != 0 {
pendingPreemptSignals.Add(-1)
}
}
// Destroy all allocated resources. After this is called, we may no
// longer take any locks.
mdestroy(mp)
if osStack {
// No more uses of mp, so it is safe to drop the reference.
mp.freeWait.Store(freeMRef)
// Return from mstart and let the system thread
// library free the g0 stack and terminate the thread.
return
}
// mstart is the thread's entry point, so there's nothing to
// return to. Exit the thread directly. exitThread will clear
// m.freeWait when it's done with the stack and the m can be
// reaped.
exitThread(&mp.freeWait)
}
// forEachP calls fn(p) for every P p when p reaches a GC safe point.
// If a P is currently executing code, this will bring the P to a GC
// safe point and execute fn on that P. If the P is not executing code
// (it is idle or in a syscall), this will call fn(p) directly while
// preventing the P from exiting its state. This does not ensure that
// fn will run on every CPU executing Go code, but it acts as a global
// memory barrier. GC uses this as a "ragged barrier."
//
// The caller must hold worldsema. fn must not refer to any
// part of the current goroutine's stack, since the GC may move it.
func forEachP(reason waitReason, fn func(*p)) {
systemstack(func() {
gp := getg().m.curg
// Mark the user stack as preemptible so that it may be scanned.
// Otherwise, our attempt to force all P's to a safepoint could
// result in a deadlock as we attempt to preempt a worker that's
// trying to preempt us (e.g. for a stack scan).
//
// N.B. The execution tracer is not aware of this status
// transition and handles it specially based on the
// wait reason.
casGToWaiting(gp, _Grunning, reason)
forEachPInternal(fn)
casgstatus(gp, _Gwaiting, _Grunning)
})
}
// forEachPInternal calls fn(p) for every P p when p reaches a GC safe point.
// It is the internal implementation of forEachP.
//
// The caller must hold worldsema and either must ensure that a GC is not
// running (otherwise this may deadlock with the GC trying to preempt this P)
// or it must leave its goroutine in a preemptible state before it switches
// to the systemstack. Due to these restrictions, prefer forEachP when possible.
//
//go:systemstack
func forEachPInternal(fn func(*p)) {
mp := acquirem()
pp := getg().m.p.ptr()
lock(&sched.lock)
if sched.safePointWait != 0 {
throw("forEachP: sched.safePointWait != 0")
}
sched.safePointWait = gomaxprocs - 1
sched.safePointFn = fn
// Ask all Ps to run the safe point function.
for _, p2 := range allp {
if p2 != pp {
atomic.Store(&p2.runSafePointFn, 1)
}
}
preemptall()
// Any P entering _Pidle or _Psyscall from now on will observe
// p.runSafePointFn == 1 and will call runSafePointFn when
// changing its status to _Pidle/_Psyscall.
// Run safe point function for all idle Ps. sched.pidle will
// not change because we hold sched.lock.
for p := sched.pidle.ptr(); p != nil; p = p.link.ptr() {
if atomic.Cas(&p.runSafePointFn, 1, 0) {
fn(p)
sched.safePointWait--
}
}
wait := sched.safePointWait > 0
unlock(&sched.lock)
// Run fn for the current P.
fn(pp)
// Force Ps currently in _Psyscall into _Pidle and hand them
// off to induce safe point function execution.
for _, p2 := range allp {
s := p2.status
// We need to be fine-grained about tracing here, since handoffp
// might call into the tracer, and the tracer is non-reentrant.
trace := traceAcquire()
if s == _Psyscall && p2.runSafePointFn == 1 && atomic.Cas(&p2.status, s, _Pidle) {
if trace.ok() {
// It's important that we traceRelease before we call handoffp, which may also traceAcquire.
trace.GoSysBlock(p2)
trace.ProcSteal(p2, false)
traceRelease(trace)
}
p2.syscalltick++
handoffp(p2)
} else if trace.ok() {
traceRelease(trace)
}
}
// Wait for remaining Ps to run fn.
if wait {
for {
// Wait for 100us, then try to re-preempt in
// case of any races.
//
// Requires system stack.
if notetsleep(&sched.safePointNote, 100*1000) {
noteclear(&sched.safePointNote)
break
}
preemptall()
}
}
if sched.safePointWait != 0 {
throw("forEachP: not done")
}
for _, p2 := range allp {
if p2.runSafePointFn != 0 {
throw("forEachP: P did not run fn")
}
}
lock(&sched.lock)
sched.safePointFn = nil
unlock(&sched.lock)
releasem(mp)
}
// runSafePointFn runs the safe point function, if any, for this P.
// This should be called like
//
// if getg().m.p.runSafePointFn != 0 {
// runSafePointFn()
// }
//
// runSafePointFn must be checked on any transition in to _Pidle or
// _Psyscall to avoid a race where forEachP sees that the P is running
// just before the P goes into _Pidle/_Psyscall and neither forEachP
// nor the P run the safe-point function.
func runSafePointFn() {
p := getg().m.p.ptr()
// Resolve the race between forEachP running the safe-point
// function on this P's behalf and this P running the
// safe-point function directly.
if !atomic.Cas(&p.runSafePointFn, 1, 0) {
return
}
sched.safePointFn(p)
lock(&sched.lock)
sched.safePointWait--
if sched.safePointWait == 0 {
notewakeup(&sched.safePointNote)
}
unlock(&sched.lock)
}
// When running with cgo, we call _cgo_thread_start
// to start threads for us so that we can play nicely with
// foreign code.
var cgoThreadStart unsafe.Pointer
type cgothreadstart struct {
g guintptr
tls *uint64
fn unsafe.Pointer
}
// Allocate a new m unassociated with any thread.
// Can use p for allocation context if needed.
// fn is recorded as the new m's m.mstartfn.
// id is optional pre-allocated m ID. Omit by passing -1.
//
// This function is allowed to have write barriers even if the caller
// isn't because it borrows pp.
//
//go:yeswritebarrierrec
func allocm(pp *p, fn func(), id int64) *m {
allocmLock.rlock()
// The caller owns pp, but we may borrow (i.e., acquirep) it. We must
// disable preemption to ensure it is not stolen, which would make the
// caller lose ownership.
acquirem()
gp := getg()
if gp.m.p == 0 {
acquirep(pp) // temporarily borrow p for mallocs in this function
}
// Release the free M list. We need to do this somewhere and
// this may free up a stack we can use.
if sched.freem != nil {
lock(&sched.lock)
var newList *m
for freem := sched.freem; freem != nil; {
// Wait for freeWait to indicate that freem's stack is unused.
wait := freem.freeWait.Load()
if wait == freeMWait {
next := freem.freelink
freem.freelink = newList
newList = freem
freem = next
continue
}
// Drop any remaining trace resources.
// Ms can continue to emit events all the way until wait != freeMWait,
// so it's only safe to call traceThreadDestroy at this point.
if traceEnabled() || traceShuttingDown() {
traceThreadDestroy(freem)
}
// Free the stack if needed. For freeMRef, there is
// nothing to do except drop freem from the sched.freem
// list.
if wait == freeMStack {
// stackfree must be on the system stack, but allocm is
// reachable off the system stack transitively from
// startm.
systemstack(func() {
stackfree(freem.g0.stack)
})
}
freem = freem.freelink
}
sched.freem = newList
unlock(&sched.lock)
}
mp := new(m)
mp.mstartfn = fn
mcommoninit(mp, id)
// In case of cgo or Solaris or illumos or Darwin, pthread_create will make us a stack.
// Windows and Plan 9 will layout sched stack on OS stack.
if iscgo || mStackIsSystemAllocated() {
mp.g0 = malg(-1)
} else {
mp.g0 = malg(16384 * sys.StackGuardMultiplier)
}
mp.g0.m = mp
if pp == gp.m.p.ptr() {
releasep()
}
releasem(gp.m)
allocmLock.runlock()
return mp
}
// needm is called when a cgo callback happens on a
// thread without an m (a thread not created by Go).
// In this case, needm is expected to find an m to use
// and return with m, g initialized correctly.
// Since m and g are not set now (likely nil, but see below)
// needm is limited in what routines it can call. In particular
// it can only call nosplit functions (textflag 7) and cannot
// do any scheduling that requires an m.
//
// In order to avoid needing heavy lifting here, we adopt
// the following strategy: there is a stack of available m's
// that can be stolen. Using compare-and-swap
// to pop from the stack has ABA races, so we simulate
// a lock by doing an exchange (via Casuintptr) to steal the stack
// head and replace the top pointer with MLOCKED (1).
// This serves as a simple spin lock that we can use even
// without an m. The thread that locks the stack in this way
// unlocks the stack by storing a valid stack head pointer.
//
// In order to make sure that there is always an m structure
// available to be stolen, we maintain the invariant that there
// is always one more than needed. At the beginning of the
// program (if cgo is in use) the list is seeded with a single m.
// If needm finds that it has taken the last m off the list, its job
// is - once it has installed its own m so that it can do things like
// allocate memory - to create a spare m and put it on the list.
//
// Each of these extra m's also has a g0 and a curg that are
// pressed into service as the scheduling stack and current
// goroutine for the duration of the cgo callback.
//
// It calls dropm to put the m back on the list,
// 1. when the callback is done with the m in non-pthread platforms,
// 2. or when the C thread exiting on pthread platforms.
//
// The signal argument indicates whether we're called from a signal
// handler.
//
//go:nosplit
func needm(signal bool) {
if (iscgo || GOOS == "windows") && !cgoHasExtraM {
// Can happen if C/C++ code calls Go from a global ctor.
// Can also happen on Windows if a global ctor uses a
// callback created by syscall.NewCallback. See issue #6751
// for details.
//
// Can not throw, because scheduler is not initialized yet.
writeErrStr("fatal error: cgo callback before cgo call\n")
exit(1)
}
// Save and block signals before getting an M.
// The signal handler may call needm itself,
// and we must avoid a deadlock. Also, once g is installed,
// any incoming signals will try to execute,
// but we won't have the sigaltstack settings and other data
// set up appropriately until the end of minit, which will
// unblock the signals. This is the same dance as when
// starting a new m to run Go code via newosproc.
var sigmask sigset
sigsave(&sigmask)
sigblock(false)
// getExtraM is safe here because of the invariant above,
// that the extra list always contains or will soon contain
// at least one m.
mp, last := getExtraM()
// Set needextram when we've just emptied the list,
// so that the eventual call into cgocallbackg will
// allocate a new m for the extra list. We delay the
// allocation until then so that it can be done
// after exitsyscall makes sure it is okay to be
// running at all (that is, there's no garbage collection
// running right now).
mp.needextram = last
// Store the original signal mask for use by minit.
mp.sigmask = sigmask
// Install TLS on some platforms (previously setg
// would do this if necessary).
osSetupTLS(mp)
// Install g (= m->g0) and set the stack bounds
// to match the current stack.
setg(mp.g0)
sp := getcallersp()
callbackUpdateSystemStack(mp, sp, signal)
// Should mark we are already in Go now.
// Otherwise, we may call needm again when we get a signal, before cgocallbackg1,
// which means the extram list may be empty, that will cause a deadlock.
mp.isExtraInC = false
// Initialize this thread to use the m.
asminit()
minit()
// Emit a trace event for this dead -> syscall transition,
// but only in the new tracer and only if we're not in a signal handler.
//
// N.B. the tracer can run on a bare M just fine, we just have
// to make sure to do this before setg(nil) and unminit.
var trace traceLocker
if goexperiment.ExecTracer2 && !signal {
trace = traceAcquire()
}
// mp.curg is now a real goroutine.
casgstatus(mp.curg, _Gdead, _Gsyscall)
sched.ngsys.Add(-1)
if goexperiment.ExecTracer2 && !signal {
if trace.ok() {
trace.GoCreateSyscall(mp.curg)
traceRelease(trace)
}
}
mp.isExtraInSig = signal
}
// Acquire an extra m and bind it to the C thread when a pthread key has been created.
//
//go:nosplit
func needAndBindM() {
needm(false)
if _cgo_pthread_key_created != nil && *(*uintptr)(_cgo_pthread_key_created) != 0 {
cgoBindM()
}
}
// newextram allocates m's and puts them on the extra list.
// It is called with a working local m, so that it can do things
// like call schedlock and allocate.
func newextram() {
c := extraMWaiters.Swap(0)
if c > 0 {
for i := uint32(0); i < c; i++ {
oneNewExtraM()
}
} else if extraMLength.Load() == 0 {
// Make sure there is at least one extra M.
oneNewExtraM()
}
}
// oneNewExtraM allocates an m and puts it on the extra list.
func oneNewExtraM() {
// Create extra goroutine locked to extra m.
// The goroutine is the context in which the cgo callback will run.
// The sched.pc will never be returned to, but setting it to
// goexit makes clear to the traceback routines where
// the goroutine stack ends.
mp := allocm(nil, nil, -1)
gp := malg(4096)
gp.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum
gp.sched.sp = gp.stack.hi
gp.sched.sp -= 4 * goarch.PtrSize // extra space in case of reads slightly beyond frame
gp.sched.lr = 0
gp.sched.g = guintptr(unsafe.Pointer(gp))
gp.syscallpc = gp.sched.pc
gp.syscallsp = gp.sched.sp
gp.stktopsp = gp.sched.sp
// malg returns status as _Gidle. Change to _Gdead before
// adding to allg where GC can see it. We use _Gdead to hide
// this from tracebacks and stack scans since it isn't a
// "real" goroutine until needm grabs it.
casgstatus(gp, _Gidle, _Gdead)
gp.m = mp
mp.curg = gp
mp.isextra = true
// mark we are in C by default.
mp.isExtraInC = true
mp.lockedInt++
mp.lockedg.set(gp)
gp.lockedm.set(mp)
gp.goid = sched.goidgen.Add(1)
if raceenabled {
gp.racectx = racegostart(abi.FuncPCABIInternal(newextram) + sys.PCQuantum)
}
trace := traceAcquire()
if trace.ok() {
trace.OneNewExtraM(gp)
traceRelease(trace)
}
// put on allg for garbage collector
allgadd(gp)
// gp is now on the allg list, but we don't want it to be
// counted by gcount. It would be more "proper" to increment
// sched.ngfree, but that requires locking. Incrementing ngsys
// has the same effect.
sched.ngsys.Add(1)
// Add m to the extra list.
addExtraM(mp)
}
// dropm puts the current m back onto the extra list.
//
// 1. On systems without pthreads, like Windows
// dropm is called when a cgo callback has called needm but is now
// done with the callback and returning back into the non-Go thread.
//
// The main expense here is the call to signalstack to release the
// m's signal stack, and then the call to needm on the next callback
// from this thread. It is tempting to try to save the m for next time,
// which would eliminate both these costs, but there might not be
// a next time: the current thread (which Go does not control) might exit.
// If we saved the m for that thread, there would be an m leak each time
// such a thread exited. Instead, we acquire and release an m on each
// call. These should typically not be scheduling operations, just a few
// atomics, so the cost should be small.
//
// 2. On systems with pthreads
// dropm is called while a non-Go thread is exiting.
// We allocate a pthread per-thread variable using pthread_key_create,
// to register a thread-exit-time destructor.
// And store the g into a thread-specific value associated with the pthread key,
// when first return back to C.
// So that the destructor would invoke dropm while the non-Go thread is exiting.
// This is much faster since it avoids expensive signal-related syscalls.
//
// This always runs without a P, so //go:nowritebarrierrec is required.
//
// This may run with a different stack than was recorded in g0 (there is no
// call to callbackUpdateSystemStack prior to dropm), so this must be
// //go:nosplit to avoid the stack bounds check.
//
//go:nowritebarrierrec
//go:nosplit
func dropm() {
// Clear m and g, and return m to the extra list.
// After the call to setg we can only call nosplit functions
// with no pointer manipulation.
mp := getg().m
// Emit a trace event for this syscall -> dead transition,
// but only in the new tracer.
//
// N.B. the tracer can run on a bare M just fine, we just have
// to make sure to do this before setg(nil) and unminit.
var trace traceLocker
if goexperiment.ExecTracer2 && !mp.isExtraInSig {
trace = traceAcquire()
}
// Return mp.curg to dead state.
casgstatus(mp.curg, _Gsyscall, _Gdead)
mp.curg.preemptStop = false
sched.ngsys.Add(1)
if goexperiment.ExecTracer2 && !mp.isExtraInSig {
if trace.ok() {
trace.GoDestroySyscall()
traceRelease(trace)
}
}
if goexperiment.ExecTracer2 {
// Trash syscalltick so that it doesn't line up with mp.old.syscalltick anymore.
//
// In the new tracer, we model needm and dropm and a goroutine being created and
// destroyed respectively. The m then might get reused with a different procid but
// still with a reference to oldp, and still with the same syscalltick. The next
// time a G is "created" in needm, it'll return and quietly reacquire its P from a
// different m with a different procid, which will confuse the trace parser. By
// trashing syscalltick, we ensure that it'll appear as if we lost the P to the
// tracer parser and that we just reacquired it.
//
// Trash the value by decrementing because that gets us as far away from the value
// the syscall exit code expects as possible. Setting to zero is risky because
// syscalltick could already be zero (and in fact, is initialized to zero).
mp.syscalltick--
}
// Reset trace state unconditionally. This goroutine is being 'destroyed'
// from the perspective of the tracer.
mp.curg.trace.reset()
// Flush all the M's buffers. This is necessary because the M might
// be used on a different thread with a different procid, so we have
// to make sure we don't write into the same buffer.
//
// N.B. traceThreadDestroy is a no-op in the old tracer, so avoid the
// unnecessary acquire/release of the lock.
if goexperiment.ExecTracer2 && (traceEnabled() || traceShuttingDown()) {
// Acquire sched.lock across thread destruction. One of the invariants of the tracer
// is that a thread cannot disappear from the tracer's view (allm or freem) without
// it noticing, so it requires that sched.lock be held over traceThreadDestroy.
//
// This isn't strictly necessary in this case, because this thread never leaves allm,
// but the critical section is short and dropm is rare on pthread platforms, so just
// take the lock and play it safe. traceThreadDestroy also asserts that the lock is held.
lock(&sched.lock)
traceThreadDestroy(mp)
unlock(&sched.lock)
}
mp.isExtraInSig = false
// Block signals before unminit.
// Unminit unregisters the signal handling stack (but needs g on some systems).
// Setg(nil) clears g, which is the signal handler's cue not to run Go handlers.
// It's important not to try to handle a signal between those two steps.
sigmask := mp.sigmask
sigblock(false)
unminit()
setg(nil)
// Clear g0 stack bounds to ensure that needm always refreshes the
// bounds when reusing this M.
g0 := mp.g0
g0.stack.hi = 0
g0.stack.lo = 0
g0.stackguard0 = 0
g0.stackguard1 = 0
putExtraM(mp)
msigrestore(sigmask)
}
// bindm store the g0 of the current m into a thread-specific value.
//
// We allocate a pthread per-thread variable using pthread_key_create,
// to register a thread-exit-time destructor.
// We are here setting the thread-specific value of the pthread key, to enable the destructor.
// So that the pthread_key_destructor would dropm while the C thread is exiting.
//
// And the saved g will be used in pthread_key_destructor,
// since the g stored in the TLS by Go might be cleared in some platforms,
// before the destructor invoked, so, we restore g by the stored g, before dropm.
//
// We store g0 instead of m, to make the assembly code simpler,
// since we need to restore g0 in runtime.cgocallback.
//
// On systems without pthreads, like Windows, bindm shouldn't be used.
//
// NOTE: this always runs without a P, so, nowritebarrierrec required.
//
//go:nosplit
//go:nowritebarrierrec
func cgoBindM() {
if GOOS == "windows" || GOOS == "plan9" {
fatal("bindm in unexpected GOOS")
}
g := getg()
if g.m.g0 != g {
fatal("the current g is not g0")
}
if _cgo_bindm != nil {
asmcgocall(_cgo_bindm, unsafe.Pointer(g))
}
}
// A helper function for EnsureDropM.
func getm() uintptr {
return uintptr(unsafe.Pointer(getg().m))
}
var (
// Locking linked list of extra M's, via mp.schedlink. Must be accessed
// only via lockextra/unlockextra.
//
// Can't be atomic.Pointer[m] because we use an invalid pointer as a
// "locked" sentinel value. M's on this list remain visible to the GC
// because their mp.curg is on allgs.
extraM atomic.Uintptr
// Number of M's in the extraM list.
extraMLength atomic.Uint32
// Number of waiters in lockextra.
extraMWaiters atomic.Uint32
// Number of extra M's in use by threads.
extraMInUse atomic.Uint32
)
// lockextra locks the extra list and returns the list head.
// The caller must unlock the list by storing a new list head
// to extram. If nilokay is true, then lockextra will
// return a nil list head if that's what it finds. If nilokay is false,
// lockextra will keep waiting until the list head is no longer nil.
//
//go:nosplit
func lockextra(nilokay bool) *m {
const locked = 1
incr := false
for {
old := extraM.Load()
if old == locked {
osyield_no_g()
continue
}
if old == 0 && !nilokay {
if !incr {
// Add 1 to the number of threads
// waiting for an M.
// This is cleared by newextram.
extraMWaiters.Add(1)
incr = true
}
usleep_no_g(1)
continue
}
if extraM.CompareAndSwap(old, locked) {
return (*m)(unsafe.Pointer(old))
}
osyield_no_g()
continue
}
}
//go:nosplit
func unlockextra(mp *m, delta int32) {
extraMLength.Add(delta)
extraM.Store(uintptr(unsafe.Pointer(mp)))
}
// Return an M from the extra M list. Returns last == true if the list becomes
// empty because of this call.
//
// Spins waiting for an extra M, so caller must ensure that the list always
// contains or will soon contain at least one M.
//
//go:nosplit
func getExtraM() (mp *m, last bool) {
mp = lockextra(false)
extraMInUse.Add(1)
unlockextra(mp.schedlink.ptr(), -1)
return mp, mp.schedlink.ptr() == nil
}
// Returns an extra M back to the list. mp must be from getExtraM. Newly
// allocated M's should use addExtraM.
//
//go:nosplit
func putExtraM(mp *m) {
extraMInUse.Add(-1)
addExtraM(mp)
}
// Adds a newly allocated M to the extra M list.
//
//go:nosplit
func addExtraM(mp *m) {
mnext := lockextra(true)
mp.schedlink.set(mnext)
unlockextra(mp, 1)
}
var (
// allocmLock is locked for read when creating new Ms in allocm and their
// addition to allm. Thus acquiring this lock for write blocks the
// creation of new Ms.
allocmLock rwmutex
// execLock serializes exec and clone to avoid bugs or unspecified
// behaviour around exec'ing while creating/destroying threads. See
// issue #19546.
execLock rwmutex
)
// These errors are reported (via writeErrStr) by some OS-specific
// versions of newosproc and newosproc0.
const (
failthreadcreate = "runtime: failed to create new OS thread\n"
failallocatestack = "runtime: failed to allocate stack for the new OS thread\n"
)
// newmHandoff contains a list of m structures that need new OS threads.
// This is used by newm in situations where newm itself can't safely
// start an OS thread.
var newmHandoff struct {
lock mutex
// newm points to a list of M structures that need new OS
// threads. The list is linked through m.schedlink.
newm muintptr
// waiting indicates that wake needs to be notified when an m
// is put on the list.
waiting bool
wake note
// haveTemplateThread indicates that the templateThread has
// been started. This is not protected by lock. Use cas to set
// to 1.
haveTemplateThread uint32
}
// Create a new m. It will start off with a call to fn, or else the scheduler.
// fn needs to be static and not a heap allocated closure.
// May run with m.p==nil, so write barriers are not allowed.
//
// id is optional pre-allocated m ID. Omit by passing -1.
//
//go:nowritebarrierrec
func newm(fn func(), pp *p, id int64) {
// allocm adds a new M to allm, but they do not start until created by
// the OS in newm1 or the template thread.
//
// doAllThreadsSyscall requires that every M in allm will eventually
// start and be signal-able, even with a STW.
//
// Disable preemption here until we start the thread to ensure that
// newm is not preempted between allocm and starting the new thread,
// ensuring that anything added to allm is guaranteed to eventually
// start.
acquirem()
mp := allocm(pp, fn, id)
mp.nextp.set(pp)
mp.sigmask = initSigmask
if gp := getg(); gp != nil && gp.m != nil && (gp.m.lockedExt != 0 || gp.m.incgo) && GOOS != "plan9" {
// We're on a locked M or a thread that may have been
// started by C. The kernel state of this thread may
// be strange (the user may have locked it for that
// purpose). We don't want to clone that into another
// thread. Instead, ask a known-good thread to create
// the thread for us.
//
// This is disabled on Plan 9. See golang.org/issue/22227.
//
// TODO: This may be unnecessary on Windows, which
// doesn't model thread creation off fork.
lock(&newmHandoff.lock)
if newmHandoff.haveTemplateThread == 0 {
throw("on a locked thread with no template thread")
}
mp.schedlink = newmHandoff.newm
newmHandoff.newm.set(mp)
if newmHandoff.waiting {
newmHandoff.waiting = false
notewakeup(&newmHandoff.wake)
}
unlock(&newmHandoff.lock)
// The M has not started yet, but the template thread does not
// participate in STW, so it will always process queued Ms and
// it is safe to releasem.
releasem(getg().m)
return
}
newm1(mp)
releasem(getg().m)
}
func newm1(mp *m) {
if iscgo {
var ts cgothreadstart
if _cgo_thread_start == nil {
throw("_cgo_thread_start missing")
}
ts.g.set(mp.g0)
ts.tls = (*uint64)(unsafe.Pointer(&mp.tls[0]))
ts.fn = unsafe.Pointer(abi.FuncPCABI0(mstart))
if msanenabled {
msanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts))
}
if asanenabled {
asanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts))
}
execLock.rlock() // Prevent process clone.
asmcgocall(_cgo_thread_start, unsafe.Pointer(&ts))
execLock.runlock()
return
}
execLock.rlock() // Prevent process clone.
newosproc(mp)
execLock.runlock()
}
// startTemplateThread starts the template thread if it is not already
// running.
//
// The calling thread must itself be in a known-good state.
func startTemplateThread() {
if GOARCH == "wasm" { // no threads on wasm yet
return
}
// Disable preemption to guarantee that the template thread will be
// created before a park once haveTemplateThread is set.
mp := acquirem()
if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) {
releasem(mp)
return
}
newm(templateThread, nil, -1)
releasem(mp)
}
// templateThread is a thread in a known-good state that exists solely
// to start new threads in known-good states when the calling thread
// may not be in a good state.
//
// Many programs never need this, so templateThread is started lazily
// when we first enter a state that might lead to running on a thread
// in an unknown state.
//
// templateThread runs on an M without a P, so it must not have write
// barriers.
//
//go:nowritebarrierrec
func templateThread() {
lock(&sched.lock)
sched.nmsys++
checkdead()
unlock(&sched.lock)
for {
lock(&newmHandoff.lock)
for newmHandoff.newm != 0 {
newm := newmHandoff.newm.ptr()
newmHandoff.newm = 0
unlock(&newmHandoff.lock)
for newm != nil {
next := newm.schedlink.ptr()
newm.schedlink = 0
newm1(newm)
newm = next
}
lock(&newmHandoff.lock)
}
newmHandoff.waiting = true
noteclear(&newmHandoff.wake)
unlock(&newmHandoff.lock)
notesleep(&newmHandoff.wake)
}
}
// Stops execution of the current m until new work is available.
// Returns with acquired P.
func stopm() {
gp := getg()
if gp.m.locks != 0 {
throw("stopm holding locks")
}
if gp.m.p != 0 {
throw("stopm holding p")
}
if gp.m.spinning {
throw("stopm spinning")
}
lock(&sched.lock)
mput(gp.m)
unlock(&sched.lock)
mPark()
acquirep(gp.m.nextp.ptr())
gp.m.nextp = 0
}
func mspinning() {
// startm's caller incremented nmspinning. Set the new M's spinning.
getg().m.spinning = true
}
// Schedules some M to run the p (creates an M if necessary).
// If p==nil, tries to get an idle P, if no idle P's does nothing.
// May run with m.p==nil, so write barriers are not allowed.
// If spinning is set, the caller has incremented nmspinning and must provide a
// P. startm will set m.spinning in the newly started M.
//
// Callers passing a non-nil P must call from a non-preemptible context. See
// comment on acquirem below.
//
// Argument lockheld indicates whether the caller already acquired the
// scheduler lock. Callers holding the lock when making the call must pass
// true. The lock might be temporarily dropped, but will be reacquired before
// returning.
//
// Must not have write barriers because this may be called without a P.
//
//go:nowritebarrierrec
func startm(pp *p, spinning, lockheld bool) {
// Disable preemption.
//
// Every owned P must have an owner that will eventually stop it in the
// event of a GC stop request. startm takes transient ownership of a P
// (either from argument or pidleget below) and transfers ownership to
// a started M, which will be responsible for performing the stop.
//
// Preemption must be disabled during this transient ownership,
// otherwise the P this is running on may enter GC stop while still
// holding the transient P, leaving that P in limbo and deadlocking the
// STW.
//
// Callers passing a non-nil P must already be in non-preemptible
// context, otherwise such preemption could occur on function entry to
// startm. Callers passing a nil P may be preemptible, so we must
// disable preemption before acquiring a P from pidleget below.
mp := acquirem()
if !lockheld {
lock(&sched.lock)
}
if pp == nil {
if spinning {
// TODO(prattmic): All remaining calls to this function
// with _p_ == nil could be cleaned up to find a P
// before calling startm.
throw("startm: P required for spinning=true")
}
pp, _ = pidleget(0)
if pp == nil {
if !lockheld {
unlock(&sched.lock)
}
releasem(mp)
return
}
}
nmp := mget()
if nmp == nil {
// No M is available, we must drop sched.lock and call newm.
// However, we already own a P to assign to the M.
//
// Once sched.lock is released, another G (e.g., in a syscall),
// could find no idle P while checkdead finds a runnable G but
// no running M's because this new M hasn't started yet, thus
// throwing in an apparent deadlock.
// This apparent deadlock is possible when startm is called
// from sysmon, which doesn't count as a running M.
//
// Avoid this situation by pre-allocating the ID for the new M,
// thus marking it as 'running' before we drop sched.lock. This
// new M will eventually run the scheduler to execute any
// queued G's.
id := mReserveID()
unlock(&sched.lock)
var fn func()
if spinning {
// The caller incremented nmspinning, so set m.spinning in the new M.
fn = mspinning
}
newm(fn, pp, id)
if lockheld {
lock(&sched.lock)
}
// Ownership transfer of pp committed by start in newm.
// Preemption is now safe.
releasem(mp)
return
}
if !lockheld {
unlock(&sched.lock)
}
if nmp.spinning {
throw("startm: m is spinning")
}
if nmp.nextp != 0 {
throw("startm: m has p")
}
if spinning && !runqempty(pp) {
throw("startm: p has runnable gs")
}
// The caller incremented nmspinning, so set m.spinning in the new M.
nmp.spinning = spinning
nmp.nextp.set(pp)
notewakeup(&nmp.park)
// Ownership transfer of pp committed by wakeup. Preemption is now
// safe.
releasem(mp)
}
// Hands off P from syscall or locked M.
// Always runs without a P, so write barriers are not allowed.
//
//go:nowritebarrierrec
func handoffp(pp *p) {
// handoffp must start an M in any situation where
// findrunnable would return a G to run on pp.
// if it has local work, start it straight away
if !runqempty(pp) || sched.runqsize != 0 {
startm(pp, false, false)
return
}
// if there's trace work to do, start it straight away
if (traceEnabled() || traceShuttingDown()) && traceReaderAvailable() != nil {
startm(pp, false, false)
return
}
// if it has GC work, start it straight away
if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) {
startm(pp, false, false)
return
}
// no local work, check that there are no spinning/idle M's,
// otherwise our help is not required
if sched.nmspinning.Load()+sched.npidle.Load() == 0 && sched.nmspinning.CompareAndSwap(0, 1) { // TODO: fast atomic
sched.needspinning.Store(0)
startm(pp, true, false)
return
}
lock(&sched.lock)
if sched.gcwaiting.Load() {
pp.status = _Pgcstop
sched.stopwait--
if sched.stopwait == 0 {
notewakeup(&sched.stopnote)
}
unlock(&sched.lock)
return
}
if pp.runSafePointFn != 0 && atomic.Cas(&pp.runSafePointFn, 1, 0) {
sched.safePointFn(pp)
sched.safePointWait--
if sched.safePointWait == 0 {
notewakeup(&sched.safePointNote)
}
}
if sched.runqsize != 0 {
unlock(&sched.lock)
startm(pp, false, false)
return
}
// If this is the last running P and nobody is polling network,
// need to wakeup another M to poll network.
if sched.npidle.Load() == gomaxprocs-1 && sched.lastpoll.Load() != 0 {
unlock(&sched.lock)
startm(pp, false, false)
return
}
// The scheduler lock cannot be held when calling wakeNetPoller below
// because wakeNetPoller may call wakep which may call startm.
when := nobarrierWakeTime(pp)
pidleput(pp, 0)
unlock(&sched.lock)
if when != 0 {
wakeNetPoller(when)
}
}
// Tries to add one more P to execute G's.
// Called when a G is made runnable (newproc, ready).
// Must be called with a P.
func wakep() {
// Be conservative about spinning threads, only start one if none exist
// already.
if sched.nmspinning.Load() != 0 || !sched.nmspinning.CompareAndSwap(0, 1) {
return
}
// Disable preemption until ownership of pp transfers to the next M in
// startm. Otherwise preemption here would leave pp stuck waiting to
// enter _Pgcstop.
//
// See preemption comment on acquirem in startm for more details.
mp := acquirem()
var pp *p
lock(&sched.lock)
pp, _ = pidlegetSpinning(0)
if pp == nil {
if sched.nmspinning.Add(-1) < 0 {
throw("wakep: negative nmspinning")
}
unlock(&sched.lock)
releasem(mp)
return
}
// Since we always have a P, the race in the "No M is available"
// comment in startm doesn't apply during the small window between the
// unlock here and lock in startm. A checkdead in between will always
// see at least one running M (ours).
unlock(&sched.lock)
startm(pp, true, false)
releasem(mp)
}
// Stops execution of the current m that is locked to a g until the g is runnable again.
// Returns with acquired P.
func stoplockedm() {
gp := getg()
if gp.m.lockedg == 0 || gp.m.lockedg.ptr().lockedm.ptr() != gp.m {
throw("stoplockedm: inconsistent locking")
}
if gp.m.p != 0 {
// Schedule another M to run this p.
pp := releasep()
handoffp(pp)
}
incidlelocked(1)
// Wait until another thread schedules lockedg again.
mPark()
status := readgstatus(gp.m.lockedg.ptr())
if status&^_Gscan != _Grunnable {
print("runtime:stoplockedm: lockedg (atomicstatus=", status, ") is not Grunnable or Gscanrunnable\n")
dumpgstatus(gp.m.lockedg.ptr())
throw("stoplockedm: not runnable")
}
acquirep(gp.m.nextp.ptr())
gp.m.nextp = 0
}
// Schedules the locked m to run the locked gp.
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func startlockedm(gp *g) {
mp := gp.lockedm.ptr()
if mp == getg().m {
throw("startlockedm: locked to me")
}
if mp.nextp != 0 {
throw("startlockedm: m has p")
}
// directly handoff current P to the locked m
incidlelocked(-1)
pp := releasep()
mp.nextp.set(pp)
notewakeup(&mp.park)
stopm()
}
// Stops the current m for stopTheWorld.
// Returns when the world is restarted.
func gcstopm() {
gp := getg()
if !sched.gcwaiting.Load() {
throw("gcstopm: not waiting for gc")
}
if gp.m.spinning {
gp.m.spinning = false
// OK to just drop nmspinning here,
// startTheWorld will unpark threads as necessary.
if sched.nmspinning.Add(-1) < 0 {
throw("gcstopm: negative nmspinning")
}
}
pp := releasep()
lock(&sched.lock)
pp.status = _Pgcstop
sched.stopwait--
if sched.stopwait == 0 {
notewakeup(&sched.stopnote)
}
unlock(&sched.lock)
stopm()
}
// Schedules gp to run on the current M.
// If inheritTime is true, gp inherits the remaining time in the
// current time slice. Otherwise, it starts a new time slice.
// Never returns.
//
// Write barriers are allowed because this is called immediately after
// acquiring a P in several places.
//
//go:yeswritebarrierrec
func execute(gp *g, inheritTime bool) {
mp := getg().m
if goroutineProfile.active {
// Make sure that gp has had its stack written out to the goroutine
// profile, exactly as it was when the goroutine profiler first stopped
// the world.
tryRecordGoroutineProfile(gp, osyield)
}
// Assign gp.m before entering _Grunning so running Gs have an
// M.
mp.curg = gp
gp.m = mp
casgstatus(gp, _Grunnable, _Grunning)
gp.waitsince = 0
gp.preempt = false
gp.stackguard0 = gp.stack.lo + stackGuard
if !inheritTime {
mp.p.ptr().schedtick++
}
// Check whether the profiler needs to be turned on or off.
hz := sched.profilehz
if mp.profilehz != hz {
setThreadCPUProfiler(hz)
}
trace := traceAcquire()
if trace.ok() {
// GoSysExit has to happen when we have a P, but before GoStart.
// So we emit it here.
if !goexperiment.ExecTracer2 && gp.syscallsp != 0 {
trace.GoSysExit(true)
}
trace.GoStart()
traceRelease(trace)
}
gogo(&gp.sched)
}
// Finds a runnable goroutine to execute.
// Tries to steal from other P's, get g from local or global queue, poll network.
// tryWakeP indicates that the returned goroutine is not normal (GC worker, trace
// reader) so the caller should try to wake a P.
func findRunnable() (gp *g, inheritTime, tryWakeP bool) {
mp := getg().m
// The conditions here and in handoffp must agree: if
// findrunnable would return a G to run, handoffp must start
// an M.
top:
pp := mp.p.ptr()
if sched.gcwaiting.Load() {
gcstopm()
goto top
}
if pp.runSafePointFn != 0 {
runSafePointFn()
}
// now and pollUntil are saved for work stealing later,
// which may steal timers. It's important that between now
// and then, nothing blocks, so these numbers remain mostly
// relevant.
now, pollUntil, _ := checkTimers(pp, 0)
// Try to schedule the trace reader.
if traceEnabled() || traceShuttingDown() {
gp := traceReader()
if gp != nil {
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, 0)
traceRelease(trace)
}
return gp, false, true
}
}
// Try to schedule a GC worker.
if gcBlackenEnabled != 0 {
gp, tnow := gcController.findRunnableGCWorker(pp, now)
if gp != nil {
return gp, false, true
}
now = tnow
}
// Check the global runnable queue once in a while to ensure fairness.
// Otherwise two goroutines can completely occupy the local runqueue
// by constantly respawning each other.
if pp.schedtick%61 == 0 && sched.runqsize > 0 {
lock(&sched.lock)
gp := globrunqget(pp, 1)
unlock(&sched.lock)
if gp != nil {
return gp, false, false
}
}
// Wake up the finalizer G.
if fingStatus.Load()&(fingWait|fingWake) == fingWait|fingWake {
if gp := wakefing(); gp != nil {
ready(gp, 0, true)
}
}
if *cgo_yield != nil {
asmcgocall(*cgo_yield, nil)
}
// local runq
if gp, inheritTime := runqget(pp); gp != nil {
return gp, inheritTime, false
}
// global runq
if sched.runqsize != 0 {
lock(&sched.lock)
gp := globrunqget(pp, 0)
unlock(&sched.lock)
if gp != nil {
return gp, false, false
}
}
// Poll network.
// This netpoll is only an optimization before we resort to stealing.
// We can safely skip it if there are no waiters or a thread is blocked
// in netpoll already. If there is any kind of logical race with that
// blocked thread (e.g. it has already returned from netpoll, but does
// not set lastpoll yet), this thread will do blocking netpoll below
// anyway.
if netpollinited() && netpollAnyWaiters() && sched.lastpoll.Load() != 0 {
if list, delta := netpoll(0); !list.empty() { // non-blocking
gp := list.pop()
injectglist(&list)
netpollAdjustWaiters(delta)
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, 0)
traceRelease(trace)
}
return gp, false, false
}
}
// Spinning Ms: steal work from other Ps.
//
// Limit the number of spinning Ms to half the number of busy Ps.
// This is necessary to prevent excessive CPU consumption when
// GOMAXPROCS>>1 but the program parallelism is low.
if mp.spinning || 2*sched.nmspinning.Load() < gomaxprocs-sched.npidle.Load() {
if !mp.spinning {
mp.becomeSpinning()
}
gp, inheritTime, tnow, w, newWork := stealWork(now)
if gp != nil {
// Successfully stole.
return gp, inheritTime, false
}
if newWork {
// There may be new timer or GC work; restart to
// discover.
goto top
}
now = tnow
if w != 0 && (pollUntil == 0 || w < pollUntil) {
// Earlier timer to wait for.
pollUntil = w
}
}
// We have nothing to do.
//
// If we're in the GC mark phase, can safely scan and blacken objects,
// and have work to do, run idle-time marking rather than give up the P.
if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) && gcController.addIdleMarkWorker() {
node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
if node != nil {
pp.gcMarkWorkerMode = gcMarkWorkerIdleMode
gp := node.gp.ptr()
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, 0)
traceRelease(trace)
}
return gp, false, false
}
gcController.removeIdleMarkWorker()
}
// wasm only:
// If a callback returned and no other goroutine is awake,
// then wake event handler goroutine which pauses execution
// until a callback was triggered.
gp, otherReady := beforeIdle(now, pollUntil)
if gp != nil {
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, 0)
traceRelease(trace)
}
return gp, false, false
}
if otherReady {
goto top
}
// Before we drop our P, make a snapshot of the allp slice,
// which can change underfoot once we no longer block
// safe-points. We don't need to snapshot the contents because
// everything up to cap(allp) is immutable.
allpSnapshot := allp
// Also snapshot masks. Value changes are OK, but we can't allow
// len to change out from under us.
idlepMaskSnapshot := idlepMask
timerpMaskSnapshot := timerpMask
// return P and block
lock(&sched.lock)
if sched.gcwaiting.Load() || pp.runSafePointFn != 0 {
unlock(&sched.lock)
goto top
}
if sched.runqsize != 0 {
gp := globrunqget(pp, 0)
unlock(&sched.lock)
return gp, false, false
}
if !mp.spinning && sched.needspinning.Load() == 1 {
// See "Delicate dance" comment below.
mp.becomeSpinning()
unlock(&sched.lock)
goto top
}
if releasep() != pp {
throw("findrunnable: wrong p")
}
now = pidleput(pp, now)
unlock(&sched.lock)
// Delicate dance: thread transitions from spinning to non-spinning
// state, potentially concurrently with submission of new work. We must
// drop nmspinning first and then check all sources again (with
// #StoreLoad memory barrier in between). If we do it the other way
// around, another thread can submit work after we've checked all
// sources but before we drop nmspinning; as a result nobody will
// unpark a thread to run the work.
//
// This applies to the following sources of work:
//
// * Goroutines added to the global or a per-P run queue.
// * New/modified-earlier timers on a per-P timer heap.
// * Idle-priority GC work (barring golang.org/issue/19112).
//
// If we discover new work below, we need to restore m.spinning as a
// signal for resetspinning to unpark a new worker thread (because
// there can be more than one starving goroutine).
//
// However, if after discovering new work we also observe no idle Ps
// (either here or in resetspinning), we have a problem. We may be
// racing with a non-spinning M in the block above, having found no
// work and preparing to release its P and park. Allowing that P to go
// idle will result in loss of work conservation (idle P while there is
// runnable work). This could result in complete deadlock in the
// unlikely event that we discover new work (from netpoll) right as we
// are racing with _all_ other Ps going idle.
//
// We use sched.needspinning to synchronize with non-spinning Ms going
// idle. If needspinning is set when they are about to drop their P,
// they abort the drop and instead become a new spinning M on our
// behalf. If we are not racing and the system is truly fully loaded
// then no spinning threads are required, and the next thread to
// naturally become spinning will clear the flag.
//
// Also see "Worker thread parking/unparking" comment at the top of the
// file.
wasSpinning := mp.spinning
if mp.spinning {
mp.spinning = false
if sched.nmspinning.Add(-1) < 0 {
throw("findrunnable: negative nmspinning")
}
// Note the for correctness, only the last M transitioning from
// spinning to non-spinning must perform these rechecks to
// ensure no missed work. However, the runtime has some cases
// of transient increments of nmspinning that are decremented
// without going through this path, so we must be conservative
// and perform the check on all spinning Ms.
//
// See https://go.dev/issue/43997.
// Check global and P runqueues again.
lock(&sched.lock)
if sched.runqsize != 0 {
pp, _ := pidlegetSpinning(0)
if pp != nil {
gp := globrunqget(pp, 0)
if gp == nil {
throw("global runq empty with non-zero runqsize")
}
unlock(&sched.lock)
acquirep(pp)
mp.becomeSpinning()
return gp, false, false
}
}
unlock(&sched.lock)
pp := checkRunqsNoP(allpSnapshot, idlepMaskSnapshot)
if pp != nil {
acquirep(pp)
mp.becomeSpinning()
goto top
}
// Check for idle-priority GC work again.
pp, gp := checkIdleGCNoP()
if pp != nil {
acquirep(pp)
mp.becomeSpinning()
// Run the idle worker.
pp.gcMarkWorkerMode = gcMarkWorkerIdleMode
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, 0)
traceRelease(trace)
}
return gp, false, false
}
// Finally, check for timer creation or expiry concurrently with
// transitioning from spinning to non-spinning.
//
// Note that we cannot use checkTimers here because it calls
// adjusttimers which may need to allocate memory, and that isn't
// allowed when we don't have an active P.
pollUntil = checkTimersNoP(allpSnapshot, timerpMaskSnapshot, pollUntil)
}
// Poll network until next timer.
if netpollinited() && (netpollAnyWaiters() || pollUntil != 0) && sched.lastpoll.Swap(0) != 0 {
sched.pollUntil.Store(pollUntil)
if mp.p != 0 {
throw("findrunnable: netpoll with p")
}
if mp.spinning {
throw("findrunnable: netpoll with spinning")
}
delay := int64(-1)
if pollUntil != 0 {
if now == 0 {
now = nanotime()
}
delay = pollUntil - now
if delay < 0 {
delay = 0
}
}
if faketime != 0 {
// When using fake time, just poll.
delay = 0
}
list, delta := netpoll(delay) // block until new work is available
// Refresh now again, after potentially blocking.
now = nanotime()
sched.pollUntil.Store(0)
sched.lastpoll.Store(now)
if faketime != 0 && list.empty() {
// Using fake time and nothing is ready; stop M.
// When all M's stop, checkdead will call timejump.
stopm()
goto top
}
lock(&sched.lock)
pp, _ := pidleget(now)
unlock(&sched.lock)
if pp == nil {
injectglist(&list)
netpollAdjustWaiters(delta)
} else {
acquirep(pp)
if !list.empty() {
gp := list.pop()
injectglist(&list)
netpollAdjustWaiters(delta)
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, 0)
traceRelease(trace)
}
return gp, false, false
}
if wasSpinning {
mp.becomeSpinning()
}
goto top
}
} else if pollUntil != 0 && netpollinited() {
pollerPollUntil := sched.pollUntil.Load()
if pollerPollUntil == 0 || pollerPollUntil > pollUntil {
netpollBreak()
}
}
stopm()
goto top
}
// pollWork reports whether there is non-background work this P could
// be doing. This is a fairly lightweight check to be used for
// background work loops, like idle GC. It checks a subset of the
// conditions checked by the actual scheduler.
func pollWork() bool {
if sched.runqsize != 0 {
return true
}
p := getg().m.p.ptr()
if !runqempty(p) {
return true
}
if netpollinited() && netpollAnyWaiters() && sched.lastpoll.Load() != 0 {
if list, delta := netpoll(0); !list.empty() {
injectglist(&list)
netpollAdjustWaiters(delta)
return true
}
}
return false
}
// stealWork attempts to steal a runnable goroutine or timer from any P.
//
// If newWork is true, new work may have been readied.
//
// If now is not 0 it is the current time. stealWork returns the passed time or
// the current time if now was passed as 0.
func stealWork(now int64) (gp *g, inheritTime bool, rnow, pollUntil int64, newWork bool) {
pp := getg().m.p.ptr()
ranTimer := false
const stealTries = 4
for i := 0; i < stealTries; i++ {
stealTimersOrRunNextG := i == stealTries-1
for enum := stealOrder.start(cheaprand()); !enum.done(); enum.next() {
if sched.gcwaiting.Load() {
// GC work may be available.
return nil, false, now, pollUntil, true
}
p2 := allp[enum.position()]
if pp == p2 {
continue
}
// Steal timers from p2. This call to checkTimers is the only place
// where we might hold a lock on a different P's timers. We do this
// once on the last pass before checking runnext because stealing
// from the other P's runnext should be the last resort, so if there
// are timers to steal do that first.
//
// We only check timers on one of the stealing iterations because
// the time stored in now doesn't change in this loop and checking
// the timers for each P more than once with the same value of now
// is probably a waste of time.
//
// timerpMask tells us whether the P may have timers at all. If it
// can't, no need to check at all.
if stealTimersOrRunNextG && timerpMask.read(enum.position()) {
tnow, w, ran := checkTimers(p2, now)
now = tnow
if w != 0 && (pollUntil == 0 || w < pollUntil) {
pollUntil = w
}
if ran {
// Running the timers may have
// made an arbitrary number of G's
// ready and added them to this P's
// local run queue. That invalidates
// the assumption of runqsteal
// that it always has room to add
// stolen G's. So check now if there
// is a local G to run.
if gp, inheritTime := runqget(pp); gp != nil {
return gp, inheritTime, now, pollUntil, ranTimer
}
ranTimer = true
}
}
// Don't bother to attempt to steal if p2 is idle.
if !idlepMask.read(enum.position()) {
if gp := runqsteal(pp, p2, stealTimersOrRunNextG); gp != nil {
return gp, false, now, pollUntil, ranTimer
}
}
}
}
// No goroutines found to steal. Regardless, running a timer may have
// made some goroutine ready that we missed. Indicate the next timer to
// wait for.
return nil, false, now, pollUntil, ranTimer
}
// Check all Ps for a runnable G to steal.
//
// On entry we have no P. If a G is available to steal and a P is available,
// the P is returned which the caller should acquire and attempt to steal the
// work to.
func checkRunqsNoP(allpSnapshot []*p, idlepMaskSnapshot pMask) *p {
for id, p2 := range allpSnapshot {
if !idlepMaskSnapshot.read(uint32(id)) && !runqempty(p2) {
lock(&sched.lock)
pp, _ := pidlegetSpinning(0)
if pp == nil {
// Can't get a P, don't bother checking remaining Ps.
unlock(&sched.lock)
return nil
}
unlock(&sched.lock)
return pp
}
}
// No work available.
return nil
}
// Check all Ps for a timer expiring sooner than pollUntil.
//
// Returns updated pollUntil value.
func checkTimersNoP(allpSnapshot []*p, timerpMaskSnapshot pMask, pollUntil int64) int64 {
for id, p2 := range allpSnapshot {
if timerpMaskSnapshot.read(uint32(id)) {
w := nobarrierWakeTime(p2)
if w != 0 && (pollUntil == 0 || w < pollUntil) {
pollUntil = w
}
}
}
return pollUntil
}
// Check for idle-priority GC, without a P on entry.
//
// If some GC work, a P, and a worker G are all available, the P and G will be
// returned. The returned P has not been wired yet.
func checkIdleGCNoP() (*p, *g) {
// N.B. Since we have no P, gcBlackenEnabled may change at any time; we
// must check again after acquiring a P. As an optimization, we also check
// if an idle mark worker is needed at all. This is OK here, because if we
// observe that one isn't needed, at least one is currently running. Even if
// it stops running, its own journey into the scheduler should schedule it
// again, if need be (at which point, this check will pass, if relevant).
if atomic.Load(&gcBlackenEnabled) == 0 || !gcController.needIdleMarkWorker() {
return nil, nil
}
if !gcMarkWorkAvailable(nil) {
return nil, nil
}
// Work is available; we can start an idle GC worker only if there is
// an available P and available worker G.
//
// We can attempt to acquire these in either order, though both have
// synchronization concerns (see below). Workers are almost always
// available (see comment in findRunnableGCWorker for the one case
// there may be none). Since we're slightly less likely to find a P,
// check for that first.
//
// Synchronization: note that we must hold sched.lock until we are
// committed to keeping it. Otherwise we cannot put the unnecessary P
// back in sched.pidle without performing the full set of idle
// transition checks.
//
// If we were to check gcBgMarkWorkerPool first, we must somehow handle
// the assumption in gcControllerState.findRunnableGCWorker that an
// empty gcBgMarkWorkerPool is only possible if gcMarkDone is running.
lock(&sched.lock)
pp, now := pidlegetSpinning(0)
if pp == nil {
unlock(&sched.lock)
return nil, nil
}
// Now that we own a P, gcBlackenEnabled can't change (as it requires STW).
if gcBlackenEnabled == 0 || !gcController.addIdleMarkWorker() {
pidleput(pp, now)
unlock(&sched.lock)
return nil, nil
}
node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
if node == nil {
pidleput(pp, now)
unlock(&sched.lock)
gcController.removeIdleMarkWorker()
return nil, nil
}
unlock(&sched.lock)
return pp, node.gp.ptr()
}
// wakeNetPoller wakes up the thread sleeping in the network poller if it isn't
// going to wake up before the when argument; or it wakes an idle P to service
// timers and the network poller if there isn't one already.
func wakeNetPoller(when int64) {
if sched.lastpoll.Load() == 0 {
// In findrunnable we ensure that when polling the pollUntil
// field is either zero or the time to which the current
// poll is expected to run. This can have a spurious wakeup
// but should never miss a wakeup.
pollerPollUntil := sched.pollUntil.Load()
if pollerPollUntil == 0 || pollerPollUntil > when {
netpollBreak()
}
} else {
// There are no threads in the network poller, try to get
// one there so it can handle new timers.
if GOOS != "plan9" { // Temporary workaround - see issue #42303.
wakep()
}
}
}
func resetspinning() {
gp := getg()
if !gp.m.spinning {
throw("resetspinning: not a spinning m")
}
gp.m.spinning = false
nmspinning := sched.nmspinning.Add(-1)
if nmspinning < 0 {
throw("findrunnable: negative nmspinning")
}
// M wakeup policy is deliberately somewhat conservative, so check if we
// need to wakeup another P here. See "Worker thread parking/unparking"
// comment at the top of the file for details.
wakep()
}
// injectglist adds each runnable G on the list to some run queue,
// and clears glist. If there is no current P, they are added to the
// global queue, and up to npidle M's are started to run them.
// Otherwise, for each idle P, this adds a G to the global queue
// and starts an M. Any remaining G's are added to the current P's
// local run queue.
// This may temporarily acquire sched.lock.
// Can run concurrently with GC.
func injectglist(glist *gList) {
if glist.empty() {
return
}
trace := traceAcquire()
if trace.ok() {
for gp := glist.head.ptr(); gp != nil; gp = gp.schedlink.ptr() {
trace.GoUnpark(gp, 0)
}
traceRelease(trace)
}
// Mark all the goroutines as runnable before we put them
// on the run queues.
head := glist.head.ptr()
var tail *g
qsize := 0
for gp := head; gp != nil; gp = gp.schedlink.ptr() {
tail = gp
qsize++
casgstatus(gp, _Gwaiting, _Grunnable)
}
// Turn the gList into a gQueue.
var q gQueue
q.head.set(head)
q.tail.set(tail)
*glist = gList{}
startIdle := func(n int) {
for i := 0; i < n; i++ {
mp := acquirem() // See comment in startm.
lock(&sched.lock)
pp, _ := pidlegetSpinning(0)
if pp == nil {
unlock(&sched.lock)
releasem(mp)
break
}
startm(pp, false, true)
unlock(&sched.lock)
releasem(mp)
}
}
pp := getg().m.p.ptr()
if pp == nil {
lock(&sched.lock)
globrunqputbatch(&q, int32(qsize))
unlock(&sched.lock)
startIdle(qsize)
return
}
npidle := int(sched.npidle.Load())
var globq gQueue
var n int
for n = 0; n < npidle && !q.empty(); n++ {
g := q.pop()
globq.pushBack(g)
}
if n > 0 {
lock(&sched.lock)
globrunqputbatch(&globq, int32(n))
unlock(&sched.lock)
startIdle(n)
qsize -= n
}
if !q.empty() {
runqputbatch(pp, &q, qsize)
}
}
// One round of scheduler: find a runnable goroutine and execute it.
// Never returns.
func schedule() {
mp := getg().m
if mp.locks != 0 {
throw("schedule: holding locks")
}
if mp.lockedg != 0 {
stoplockedm()
execute(mp.lockedg.ptr(), false) // Never returns.
}
// We should not schedule away from a g that is executing a cgo call,
// since the cgo call is using the m's g0 stack.
if mp.incgo {
throw("schedule: in cgo")
}
top:
pp := mp.p.ptr()
pp.preempt = false
// Safety check: if we are spinning, the run queue should be empty.
// Check this before calling checkTimers, as that might call
// goready to put a ready goroutine on the local run queue.
if mp.spinning && (pp.runnext != 0 || pp.runqhead != pp.runqtail) {
throw("schedule: spinning with local work")
}
gp, inheritTime, tryWakeP := findRunnable() // blocks until work is available
if debug.dontfreezetheworld > 0 && freezing.Load() {
// See comment in freezetheworld. We don't want to perturb
// scheduler state, so we didn't gcstopm in findRunnable, but
// also don't want to allow new goroutines to run.
//
// Deadlock here rather than in the findRunnable loop so if
// findRunnable is stuck in a loop we don't perturb that
// either.
lock(&deadlock)
lock(&deadlock)
}
// This thread is going to run a goroutine and is not spinning anymore,
// so if it was marked as spinning we need to reset it now and potentially
// start a new spinning M.
if mp.spinning {
resetspinning()
}
if sched.disable.user && !schedEnabled(gp) {
// Scheduling of this goroutine is disabled. Put it on
// the list of pending runnable goroutines for when we
// re-enable user scheduling and look again.
lock(&sched.lock)
if schedEnabled(gp) {
// Something re-enabled scheduling while we
// were acquiring the lock.
unlock(&sched.lock)
} else {
sched.disable.runnable.pushBack(gp)
sched.disable.n++
unlock(&sched.lock)
goto top
}
}
// If about to schedule a not-normal goroutine (a GCworker or tracereader),
// wake a P if there is one.
if tryWakeP {
wakep()
}
if gp.lockedm != 0 {
// Hands off own p to the locked m,
// then blocks waiting for a new p.
startlockedm(gp)
goto top
}
execute(gp, inheritTime)
}
// dropg removes the association between m and the current goroutine m->curg (gp for short).
// Typically a caller sets gp's status away from Grunning and then
// immediately calls dropg to finish the job. The caller is also responsible
// for arranging that gp will be restarted using ready at an
// appropriate time. After calling dropg and arranging for gp to be
// readied later, the caller can do other work but eventually should
// call schedule to restart the scheduling of goroutines on this m.
func dropg() {
gp := getg()
setMNoWB(&gp.m.curg.m, nil)
setGNoWB(&gp.m.curg, nil)
}
// checkTimers runs any timers for the P that are ready.
// If now is not 0 it is the current time.
// It returns the passed time or the current time if now was passed as 0.
// and the time when the next timer should run or 0 if there is no next timer,
// and reports whether it ran any timers.
// If the time when the next timer should run is not 0,
// it is always larger than the returned time.
// We pass now in and out to avoid extra calls of nanotime.
//
//go:yeswritebarrierrec
func checkTimers(pp *p, now int64) (rnow, pollUntil int64, ran bool) {
// If it's not yet time for the first timer, or the first adjusted
// timer, then there is nothing to do.
next := pp.timer0When.Load()
nextAdj := pp.timerModifiedEarliest.Load()
if next == 0 || (nextAdj != 0 && nextAdj < next) {
next = nextAdj
}
if next == 0 {
// No timers to run or adjust.
return now, 0, false
}
if now == 0 {
now = nanotime()
}
if now < next {
// Next timer is not ready to run, but keep going
// if we would clear deleted timers.
// This corresponds to the condition below where
// we decide whether to call clearDeletedTimers.
if pp != getg().m.p.ptr() || int(pp.deletedTimers.Load()) <= int(pp.numTimers.Load()/4) {
return now, next, false
}
}
lock(&pp.timersLock)
if len(pp.timers) > 0 {
adjusttimers(pp, now)
for len(pp.timers) > 0 {
// Note that runtimer may temporarily unlock
// pp.timersLock.
if tw := runtimer(pp, now); tw != 0 {
if tw > 0 {
pollUntil = tw
}
break
}
ran = true
}
}
// If this is the local P, and there are a lot of deleted timers,
// clear them out. We only do this for the local P to reduce
// lock contention on timersLock.
if pp == getg().m.p.ptr() && int(pp.deletedTimers.Load()) > len(pp.timers)/4 {
clearDeletedTimers(pp)
}
unlock(&pp.timersLock)
return now, pollUntil, ran
}
func parkunlock_c(gp *g, lock unsafe.Pointer) bool {
unlock((*mutex)(lock))
return true
}
// park continuation on g0.
func park_m(gp *g) {
mp := getg().m
trace := traceAcquire()
// N.B. Not using casGToWaiting here because the waitreason is
// set by park_m's caller.
casgstatus(gp, _Grunning, _Gwaiting)
if trace.ok() {
trace.GoPark(mp.waitTraceBlockReason, mp.waitTraceSkip)
traceRelease(trace)
}
dropg()
if fn := mp.waitunlockf; fn != nil {
ok := fn(gp, mp.waitlock)
mp.waitunlockf = nil
mp.waitlock = nil
if !ok {
trace := traceAcquire()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.ok() {
trace.GoUnpark(gp, 2)
traceRelease(trace)
}
execute(gp, true) // Schedule it back, never returns.
}
}
schedule()
}
func goschedImpl(gp *g, preempted bool) {
trace := traceAcquire()
status := readgstatus(gp)
if status&^_Gscan != _Grunning {
dumpgstatus(gp)
throw("bad g status")
}
casgstatus(gp, _Grunning, _Grunnable)
if trace.ok() {
if preempted {
trace.GoPreempt()
} else {
trace.GoSched()
}
traceRelease(trace)
}
dropg()
lock(&sched.lock)
globrunqput(gp)
unlock(&sched.lock)
if mainStarted {
wakep()
}
schedule()
}
// Gosched continuation on g0.
func gosched_m(gp *g) {
goschedImpl(gp, false)
}
// goschedguarded is a forbidden-states-avoided version of gosched_m.
func goschedguarded_m(gp *g) {
if !canPreemptM(gp.m) {
gogo(&gp.sched) // never return
}
goschedImpl(gp, false)
}
func gopreempt_m(gp *g) {
goschedImpl(gp, true)
}
// preemptPark parks gp and puts it in _Gpreempted.
//
//go:systemstack
func preemptPark(gp *g) {
status := readgstatus(gp)
if status&^_Gscan != _Grunning {
dumpgstatus(gp)
throw("bad g status")
}
if gp.asyncSafePoint {
// Double-check that async preemption does not
// happen in SPWRITE assembly functions.
// isAsyncSafePoint must exclude this case.
f := findfunc(gp.sched.pc)
if !f.valid() {
throw("preempt at unknown pc")
}
if f.flag&abi.FuncFlagSPWrite != 0 {
println("runtime: unexpected SPWRITE function", funcname(f), "in async preempt")
throw("preempt SPWRITE")
}
}
// Transition from _Grunning to _Gscan|_Gpreempted. We can't
// be in _Grunning when we dropg because then we'd be running
// without an M, but the moment we're in _Gpreempted,
// something could claim this G before we've fully cleaned it
// up. Hence, we set the scan bit to lock down further
// transitions until we can dropg.
casGToPreemptScan(gp, _Grunning, _Gscan|_Gpreempted)
dropg()
// Be careful about how we trace this next event. The ordering
// is subtle.
//
// The moment we CAS into _Gpreempted, suspendG could CAS to
// _Gwaiting, do its work, and ready the goroutine. All of
// this could happen before we even get the chance to emit
// an event. The end result is that the events could appear
// out of order, and the tracer generally assumes the scheduler
// takes care of the ordering between GoPark and GoUnpark.
//
// The answer here is simple: emit the event while we still hold
// the _Gscan bit on the goroutine. We still need to traceAcquire
// and traceRelease across the CAS because the tracer could be
// what's calling suspendG in the first place, and we want the
// CAS and event emission to appear atomic to the tracer.
trace := traceAcquire()
if trace.ok() {
trace.GoPark(traceBlockPreempted, 0)
}
casfrom_Gscanstatus(gp, _Gscan|_Gpreempted, _Gpreempted)
if trace.ok() {
traceRelease(trace)
}
schedule()
}
// goyield is like Gosched, but it:
// - emits a GoPreempt trace event instead of a GoSched trace event
// - puts the current G on the runq of the current P instead of the globrunq
func goyield() {
checkTimeouts()
mcall(goyield_m)
}
func goyield_m(gp *g) {
trace := traceAcquire()
pp := gp.m.p.ptr()
casgstatus(gp, _Grunning, _Grunnable)
if trace.ok() {
trace.GoPreempt()
traceRelease(trace)
}
dropg()
runqput(pp, gp, false)
schedule()
}
// Finishes execution of the current goroutine.
func goexit1() {
if raceenabled {
racegoend()
}
trace := traceAcquire()
if trace.ok() {
trace.GoEnd()
traceRelease(trace)
}
mcall(goexit0)
}
// goexit continuation on g0.
func goexit0(gp *g) {
gdestroy(gp)
schedule()
}
func gdestroy(gp *g) {
mp := getg().m
pp := mp.p.ptr()
casgstatus(gp, _Grunning, _Gdead)
gcController.addScannableStack(pp, -int64(gp.stack.hi-gp.stack.lo))
if isSystemGoroutine(gp, false) {
sched.ngsys.Add(-1)
}
gp.m = nil
locked := gp.lockedm != 0
gp.lockedm = 0
mp.lockedg = 0
gp.preemptStop = false
gp.paniconfault = false
gp._defer = nil // should be true already but just in case.
gp._panic = nil // non-nil for Goexit during panic. points at stack-allocated data.
gp.writebuf = nil
gp.waitreason = waitReasonZero
gp.param = nil
gp.labels = nil
gp.timer = nil
if gcBlackenEnabled != 0 && gp.gcAssistBytes > 0 {
// Flush assist credit to the global pool. This gives
// better information to pacing if the application is
// rapidly creating an exiting goroutines.
assistWorkPerByte := gcController.assistWorkPerByte.Load()
scanCredit := int64(assistWorkPerByte * float64(gp.gcAssistBytes))
gcController.bgScanCredit.Add(scanCredit)
gp.gcAssistBytes = 0
}
dropg()
if GOARCH == "wasm" { // no threads yet on wasm
gfput(pp, gp)
return
}
if mp.lockedInt != 0 {
print("invalid m->lockedInt = ", mp.lockedInt, "\n")
throw("internal lockOSThread error")
}
gfput(pp, gp)
if locked {
// The goroutine may have locked this thread because
// it put it in an unusual kernel state. Kill it
// rather than returning it to the thread pool.
// Return to mstart, which will release the P and exit
// the thread.
if GOOS != "plan9" { // See golang.org/issue/22227.
gogo(&mp.g0.sched)
} else {
// Clear lockedExt on plan9 since we may end up re-using
// this thread.
mp.lockedExt = 0
}
}
}
// save updates getg().sched to refer to pc and sp so that a following
// gogo will restore pc and sp.
//
// save must not have write barriers because invoking a write barrier